1.fewer改less,pollution为不可数n.
2.able前加be,be able to do sth.
3.what 改how
4.maybe 改may be
5.not后加to,tell sb.to do sth.
6.am改was,前面为thought,事态一致
7.are改were,后面“当他来的时候”为过去时,事态要一致
8.If改When,句意:当他去学校的时候,他看到.
9.was I 改 I was ,间接引语
10.surprise改surprised
11.finishes 改finishing,after doing sth.
12.is改are,books为复数
13.have 改did,疑问词when和后面的回答都表时间点,应用一般过去时,不用完成时
14.half前加since,现在完成时