用动词的适当形式填空。 1. I don't know if he (come) tomorrow. If he (come), I will tell you. 2. He (learn) two thousand English words by the end of last year. 3. When I saw her, she was busy (write) a letter. 4. Last night I (invite) to my teacher's home for dinner. 5. The workers are made (work) fourteen hours a day.