两种说法都可以，不过是用前边一种说法I 主语think谓语 your brother宾 a clever boy宾补，at the meeting状语, we主语 selected 谓语 him 宾语 monitor宾补
这时这两个句子都是个单句， a clever boy 和 monitor是宾语补足语。而用这种说法的时候I think your brother is a clever boy?句子是一个含有宾语从句的复合句。
再如
we call him the prince of gymnasts 我们叫他体操王子。
My father names my pet Lily.
we elected him our monitor.
