So difficult ______ it to work out the problem that I decided to ask Tom for advice.

Mr. Smith was ________ UNICEF officer. He came to the village and changed the poor girl’s life.

I don’tknow if I himthis evening. If I him,I will give the novel to him.

Excuse me, is this the right way to the Peking University— Sorry, I am not sure. But it ______ be.

While the boy ______ down the street, the UFO_____ .