Hello, this is Jack. May I speak to Tom?– Sorry, he isn’t in at the moment. If he _______ back, I’ll ask him to call you back.
There are_________ students in my school._________ students in my school is over 5000.
English is too hard for me to study well. I don’t want to learn it any more.－Don’t . It is useful in the future.
Everyone knows that _____ sun is in the center of the solar system（太阳系）
Though she is _______ at home, she never feels ________.