Everyone in our class is listening to the teacher now.
Everyone是单数 用is
I have a few postcards.You can use them.
如果用few而不是a few,说明你没有多少postcards
I have something good to tell you.
Somthing + 形容词 固定短语 意思就是形容词+someting的意思
The boy who is called Jim is my friend.
如果不加who,这句话有两个谓语 calls 和 is,不符合句子结构
who is called Jim 是从句,也就是句子里面的句子,这个句子是形容jim的
那个叫jim的男孩是我的朋友.