I think English is __________ unimportant subject.— I don’t think so. It is __________ useful tool when we talk with foreigners.

Mike is really a polite boy.— Yes. He ________ “Good morning” to meevery day.

Why didn’t you call me this morning?——I ______ call you. I called you all the morning, but I couldn’t ______.

What does P．O．_________?—-Poster order, I guess．

________________________—It is nine dollars.