C

句意为：母亲总是抱怨孩子们的鞋磨损得很快。find out 发现，查出（真理/真相）wash out 洗掉，破产 set out 出发，着手wear out用坏； 穿破； （使）筋疲力尽； 耗尽。

【考点定位】动词短语语境运用考查 wear out 短语可以在必修四第三单元A master of nonverbal humour 一文中The tramp, a poor, homeless man with a moustache, wore large trousers, worn-out shoes and a small round black hat.句子里找到踪影。即形容词worn-out。动词短语wear out有“用坏； 穿破； （使）筋疲力尽； 耗尽”之意。如：Clothing seems to wear out in no time nowadays。（现在的衣服好像很快就穿破了。）The past few days had really worn him out. （过去的几天真把他给累坏了。）No matter how often they turn up, their welcome never wears out. （不管他们多久露面一次，都永远那么受欢迎。）