Kai lived on the third floor of an apartment building. Every Tuesday, muddy footprints covered the back stairs. The prints started at the back door. They stopped right at the mail room.
凯住在一栋公寓楼的三楼。 每个星期二，后楼梯上都会布满泥脚印。 脚印从后门开始。 一直延伸到收发室门口才停下。
Kai first thought a neighbor made the mess. He asked around, but no one knew. The mystery bothered him every single week.
凯起初以为是哪个邻居弄脏的。 他向大家打听，可是没人知道。 这个谜团每个星期都让他心里不踏实。
One rainy Tuesday, Kai got up early. He sat near the back door with his coffee. At seven o'clock, someone opened the door.
一个下雨的星期二，凯起了个大早。 他端着咖啡，坐在后门附近。 七点钟，有人推开了门。
A mail carrier walked in with a big bag. Rain dripped from her yellow raincoat. Her boots left wet, muddy prints on the floor.
一位邮递员背着一个大包走了进来。 雨水从她的黄色雨衣上滴落下来。 她的靴子在地上留下了湿漉漉的泥脚印。
"Good morning," Kai said with a smile.
“早上好。”凯笑着说。
"Good morning," the mail carrier said. "Sorry about the mud."
“早上好，”邮递员说，“不好意思，弄了一地泥。”
"This door saves time on rainy days," she said. "The front entrance is far around the building."
“下雨天走这扇门能省时间，”她说， “前门绕着楼走，太远了。”
"That makes sense," Kai said. "I was just curious."
“原来如此，”凯说，“我只是好奇。”
"I always try to wipe my boots," she said. "But the front mat sits too far away."
“我总是尽量把靴子擦干净，”她说， “可是前门的地垫离得太远了。”
Kai had an idea right away. "What about a mat right here?" he asked.
凯马上有了个主意。 “这里放一块地垫怎么样？”他问。
The mail carrier smiled and nodded. "That would help a lot," she said.
邮递员笑着点了点头。 “那可帮了大忙了，”她说。
Kai bought a thick mat that same day. He put it next to the back door.
凯当天就买了一块厚实的地垫。 他把它放在后门旁边。
The next Tuesday, Kai checked the stairs. The floor was clean and dry. A few small, damp marks sat on the mat.
下一个星期二，凯去看了看楼梯。 地面干净又干爽。 地垫上只留着几个小小的潮湿印子。
Kai smiled and picked up his coffee. The stairs stayed clean every Tuesday after that.
凯笑了笑，端起了他的咖啡。 从那以后，每个星期二楼梯都保持得干干净净。
