当你称呼李老师（男）时，应如何称呼________.

“May I speak to your manager Mr. Williams at five o’clock tonight?”— “I’m sorry. Mr Williams ________ to a conference by then.”

The engineer ______my father works is about 50 years old.

Man must produce more grain to support the _____ growing population on earth

_____ with different medicines, thepatient hasn’t recovered from the mysterious illness yet