Some friends tried to settle the quarrel between Mr. and Mrs. Smith without hurting the feeling of _____, but failed.

I am so tired. I don’t want to do ________ now. 

Many Chinese students found______ difficult to learn English grammar.

One of the students hasn’t prepared _____ lessons very well.

- There must be a dozen pens in this house but I can never find one when I need one.- Keep looking._____ is sure to turn up.