You’re_____your time trying to persuade him. He’ll never join us.
Jack is late again. It isof him to keep others waiting.
Jack, who pretended, heard, however, every word that was said.
The old man __________ in Tibet for two years as a volunteer teacher;it is an experience he often mentions.
Qian Xuesen tried many times _________ he found the solution to the puzzle about space technology.
Thosethe exam cheat mustanother exam tomorrow afternoon.