1、Class 3 was all out when the door opened。
2、The police is searching for the murderer last night。
3、He is one of the students，who，I’m sure，always do his best。
4、Our headmaster and secretary are kind and strict。
1、Class 3 (was) all out when the door opened。应该用were复数嘛2、The police (is) searching for the murderer last night\应该用were同样复数并且是过去进行时(police和Class 都是集体名词在有的情况下是复数有时是单数这个就要靠理解了~比如:class is great这里就要用三单了如果是class are herE这里就看成复数了也就是看这个单词表示的是什么)3、He is one of the students，who，I’m sure，always (do) his best。第三人称单数额用does4、...
