While ________ to foreigners，you must try your best to make yourself ________.

They became good friends during the war, and since then their lifelong friendship has______ tests of life and death.

The reason for his success is ______ he worked very hard.

We collected a lot of books to get the necessary information but only half _________helpful, so we failed to finish the work.

Excuse me, Could you tell__________ —Yes. Go along this street and you will find it on your left.