A great excuse 合适的借口

To make the rush hour easier, our small grocery1 store has a rule for children returning soft-drink bottles:
NO BOTTLES ACCEPTED AFTER FIVE O'CLOCK
One day neat closing time at 6:30, four young children arrived with bottles. Wanting to put a stop to this habit, I sternly2 asked each child if he was aware of the rules. Three shook their heads no, but the youngest said he knew. "Why then." I asked, "have you brought me these bottles?"
"I can't tell time yet." He said.
为了缓解购物高峰，我们这个小水果店为孩子们退饮料瓶做了如下规定：
五点钟以后不收瓶子
快到六点半下班的时候，四个孩子来退瓶子。为了制止他们的这个习惯，我故意很严肃的问每个孩子是否知道我们的规定。其中三个孩子都摇头表示不知道。只有那个最小的说他知道。“那你为什么还在这个时间来退瓶子呢？”我问他。
“我还不认识表呢！”他说。