The canteen on the building site smelled of soup and wet boots. At noon it was full of loud workers. They wore orange jackets and dusty boots.
工地食堂里弥漫着汤和湿靴子的味道。中午的时候，里面坐满了吵吵嚷嚷的工人。他们穿着橙色的外套，靴子上落满灰尘。
Gabi sat alone at the back table. In front of her stood a stack of paper planes. There were twenty, and she folded them herself that morning.
加比独自坐在最里面的桌子旁。她面前放着一摞纸飞机。一共二十架，都是她今天早上自己折的。
Salma, the site manager, walked over with a tray. She looked at the planes and raised one eyebrow. "Is it a hobby?"
工地经理萨尔玛端着托盘走了过来。她看了看那些飞机，挑起一边眉毛。“这是爱好吗？”
"It is a test," Gabi said. "Sit down. I need your help."
“这是个测试，”加比说，“坐下。我需要你帮忙。”
Salma sat. Outside the window, a small gray drone rose from the yard. It carried a box of screws up to the third floor. It made a soft buzzing sound, like a big fly.
萨尔玛坐下了。窗外，一架灰色的小无人机从院子里升起。它载着一盒螺丝往三楼飞去。它发出轻轻的嗡嗡声，像一只大苍蝇。
"The delivery drones are good," Salma said. "But they have no safe place to land. Tomorrow, the company sends the new ones. We need a landing pad for them by tonight."
“送货无人机很好用，”萨尔玛说，“但它们没有安全的降落地点。明天公司就会把新的送来。今晚之前我们得给它们找一块降落台。”
"I know," Gabi said. "I am the one who must choose where it goes."
“我知道，”加比说，“该决定它放在哪儿的人是我。”
Gabi was the site's drone chief. Last year, she was a crane driver. Then the company brought in flying machines. They asked her to learn them. She learned fast, and she liked the work.
加比是工地的无人机负责人。去年她还是塔吊司机。后来公司引进了飞行机器。他们让她去学。她学得很快，也喜欢这份工作。
"There are two places," she said. She put two fingers on the table. "The roof of the canteen is close to the tower. The drones save four minutes on each trip."
“有两个地方，”她说。她把两根手指放在桌上。“食堂的屋顶离塔楼很近。无人机每跑一趟能省四分钟。”
"That is a lot of time," Salma said.
“那可是很多时间，”萨尔玛说。
"But the roof is above our heads. A drone can fall here." Gabi pointed at the ceiling. "The other place is the gravel yard behind the fence. It is safe, but far. We lose time on every trip."
“但屋顶就在我们头顶上。无人机可能会掉在这里。”加比指了指天花板。“另一个地方是围栏后面的碎石场。它很安全，但是很远。每一趟我们都要损失时间。”
Salma ate some soup and thought. "Both are okay. Take the roof. Time matters."
萨尔玛喝了几口汤，思考着。“两个都行。选屋顶吧。时间重要。”
"Or take the yard. Safety is safety." Gabi sighed. "That is the problem. Both are okay. I cannot see a wrong choice."
“或者选碎石场。安全就是安全。”加比叹了口气。“这就是问题所在。两个都行。我看不出哪个选择是错的。”
"So how do the planes help?"
“那纸飞机怎么帮得上忙？”
"Air is invisible," Gabi said. "But a paper plane shows you where it goes. I want to see how the air moves above each place."
“空气是看不见的，”加比说，“但纸飞机能告诉你它飞向哪里。我想看看每个地方上方的空气是怎么流动的。”
Salma smiled. "That is clever. Or very silly."
萨尔玛笑了。“这很聪明。或者很傻。”
"We will see," Gabi said.
“我们走着瞧，”加比说。
They took the planes. They went up the stairs to the canteen roof. The wind was calm there, with a soft push from the left. Behind them, the crane turned slowly against the sky.
她们拿上飞机，走楼梯上了食堂屋顶。那里风很平静，左边吹来轻轻的一股力。在她们身后，塔吊正缓缓转过天空。
Gabi stood at the edge. She held the first plane high. "Watch where it goes."
加比站在屋顶边缘。她把第一架飞机高高举起。“看它飞向哪里。”
She threw it. The plane flew straight for a few seconds. Then it turned in a tight circle. It fell back to the roof.
她扔了出去。飞机笔直地飞了几秒。然后绕出一个紧紧的圆圈。又掉回了屋顶。
"One," Salma counted.
“一，”萨尔玛数道。
Gabi threw the second one. It also turned. The third dropped like a stone. The fourth flew upward, then stopped and fell back. By the tenth plane, Salma stopped counting out loud.
加比扔出第二架。它也转了弯。第三架像石头一样掉了下去。第四架先往上飞，然后停住，掉了回来。到了第十架，萨尔玛不再出声数了。
"The roof is a mess," Gabi said. "Look. The air bends around the canteen wall. It goes up, then down, then around. A drone shakes."
“屋顶乱得一塌糊涂，”加比说，“你看。空气绕着食堂的墙拐弯。先上去，再下来，再绕一圈。无人机会抖。”
"But the planes are light. Drones are heavy."
“可是纸飞机很轻。无人机很重。”
"Drones are heavy," Gabi agreed. "But they have small, quick wings. They feel the air very strongly. It is the same problem, only bigger."
“无人机是很重，”加比同意道，“但它们的翼小而灵敏。它们对空气的感觉非常强烈。是同样的问题，只是更大。”
Salma looked at the fallen planes. Four lay near the edge. One hung from a pipe. "So the roof is a bad place."
萨尔玛看着掉落的飞机。四架躺在边缘附近。一架挂在一根管子上。“所以屋顶是个糟糕的地方。”
"A bad place for a landing, yes. A big wall can fix it. That costs money and time." Gabi picked up the planes, one by one. "Now the yard."
“作为降落点，是的，很糟糕。可以用一堵大墙来解决。但那要花钱，也要花时间。”加比把飞机一架一架捡起来。“现在去碎石场。”
They went down again. The yard was a wide, flat square of gray gravel. It lay behind the metal fence. There was nothing tall near it except a pile of pipes.
她们又下楼去了。碎石场是一大块平坦的灰色碎石方场。它在金属围栏后面。附近除了一堆管子，没有任何高大的东西。
Gabi walked to the middle. She held up the first plane from the second batch.
加比走到中间。她举起第二批的第一架飞机。
It flew like a bird. It went straight, slow, and long. It crossed the whole yard and landed softly near the fence.
它像鸟儿一样飞了出去。笔直，缓慢，悠长。它飞过了整个场地，轻轻落在围栏附近。
"Oh," Salma said.
“哦，”萨尔玛说。
The second plane did the same. And the third. Gabi threw ten planes, and nine of them flew smoothly. One hit the pile of pipes. That was her own bad throw.
第二架也是如此。第三架也是。加比扔了十架，其中九架飞得平稳顺畅。有一架撞上了那堆管子。那是她自己扔得不好。
"The yard is calm," Gabi said. "The air is clean here."
“碎石场很平静，”加比说，“这里的空气很干净。”
"But it is far from the tower."
“可是离塔楼很远。”
"Yes. It is four minutes slower on every trip." Gabi picked up a plane. "But it never shakes, never falls, and never lands on your lunch. And we can move the pipes."
“是的。每一趟要慢四分钟。”加比拿起一架飞机。“但它从不抖动，从不坠落，也永远不会掉在你的午饭上。而且管子可以挪走。”
Salma was silent for a while. She looked at the roof. She looked at the yard. Then she looked at the tiny plane.
萨尔玛沉默了好一阵。她看看屋顶。看看碎石场。然后看着那架小小的飞机。
"You had the answer before you came here," she said. "Tell me the truth."
“你在来这里之前就有答案了，”她说，“跟我说实话。”
"No." Gabi shook her head. "I had two good choices. I wanted to feel the difference, not just count it. Now I know why I choose the yard. I do not just guess."
“没有，”加比摇摇头，“我有两个好选择。我想感受到差别，而不是光靠数字。现在我知道为什么选碎石场了。我不是在瞎猜。”
Salma took out her phone and typed a message to the office. Then she wrote a second message to the pipe crew. "The yard it is. I will tell the pipe team to move their stack."
萨尔玛掏出手机，给办公室发了一条消息。接着又给管道组发了第二条。“那就定碎石场了。我会告诉管道组把他们那堆管子挪开。”
"Thank you."
“谢谢你。”
"And I will tell the cook his roof is safe." Salma grinned. "He was afraid of the drones."
“我还要告诉厨师，他的屋顶是安全的。”萨尔玛咧嘴笑了。“他一直害怕无人机。”
They walked slowly back to the canteen. The afternoon sun was warm on the gravel. One last plane lay in the yard. Its nose was in the stones.
她们慢慢走回食堂。午后的阳光洒在碎石上，暖洋洋的。院子里还躺着最后一架飞机。它的机头插在石头里。
Gabi picked it up. She looked at it for a moment. Then she put it in her pocket.
加比把它捡了起来。她看了它一会儿。然后把它放进了口袋。
Salma opened the canteen door. The smell of soup came out. "One more thing," she said. "The new drones are twice as big. Does the yard work for them too?"
萨尔玛推开食堂的门。汤的香味飘了出来。“还有一件事，”她说，“新的无人机比这些大一倍。碎石场对它们也行得通吗？”
