观察句子: 1. By the end of last month, the work had been finished. 2. My computer had been all right till last Monday. 3. Before father came back, the kids had already gone to bed. 4. The students of Class 1 were very happy because they had won the basketball match. 5. The boy was reminded that his homework had not been handed in. 6.They left after the door had been locked.
注意时态、语态和时间状语