近年来，越来越多的居民外出旅游度假，黄金周首日，全国铁路发送旅客1253.7万人次，同比增长6.9％，再创铁路单日旅客发送量历史新高。出现这种消费现象和行为的根本原因是（   ）

Tom hasn't appeared for 10 days. So I promise his parents: “I'll report back, the moment I ________ him.”

①I'd like to go with you, ____ I'm too busy．

②It was only five minutes'walk from here, ____ we didn't take a taxi．

③ Suddenly he tripped____fell．____ he woke up．

④You can go on foot, ____ you like．It's not far．

⑤I fell off my bike last Saturday,____ hurt my foot．

一群蚂蚁群聚生活，个体之间有明确分工，同时通力合作，它们之间的关系是（  ）

某码头上有20名工人装载一批货物，已知每人往一艘轮船上装载2吨货物，装载完毕恰好用了6天，轮船到达目的地后，另一批工人开始卸货，计划平均每天卸货v吨，刚要卸货时遇到紧急情况，要求船上的货物卸载完毕不超过4天，则这批工人实际每天至少应卸货（　　）