Why didn’t you go to the movie yesterday? —Because I_________it before.

Listen! Is Kitty in the next room? —No, it ______ be Kitty. She has gone to Beijing.

Although many great people ever failed, they never_______ and managed to succeed.

It is thought that one billion people in the world,_____ is half the world’s workers, earn their living by farming.

You see, “Food Safety” receives thousands of Internet hits a day.—Obviously, it has become one of the _________ topics recently.