Is the girl in the red skirt your sister?—No. It _______ be her. She has flown to Australia.

It is reported that the United States uses ______ energy as the whole of Europe.

So difficult _____ it to adjust to an English-speaking environment that he determined to learn English hard.

What would you do if you _____ a million dollars?- I’d give half of it to charity.

Did you go to school yesterday?— Yes, I did. But I was late. When I got to school, Mr. Zhang __________his lessons.