She looks very sad. I want to help her, but I just don’t know ____ to do it.
He went to England by______ plane.
---How do you study for a test? ---________.
----Excuse me, sir. Could you tell me________ ? ----Sorry, I don’t know.
You’ll like it if you ______ on the sea.
In fact, the Englishman didn’t understand the three questions ___________ were asked in French.