Why did they help Mrs Brown with her work? – Because she was _____.

When you have difficulty, do remember to _________. Two heads are better than one.

It was raining ________when we were on our way home.

Look at that girl! Is it Susan? –No, it _______ be her. She went to her hometown just now.

He likes low-carbon life. He lives in the house ________ he built himself out of trash.