最佳答案：是动词短语，例如：1.She was held back by some sense of self-preservation.一种自我保护意识使她没有贸然行动。2.He knew that if h
是动词短语，例如：
1.She was held back by some sense of self-preservation.一种自我保护意识使她没有贸然行动。
2.He knew that if he wasn't back by midnight, his parents would have something to say about it.他知道，要是他半夜还不回去，父母就会不高兴。
3.She should be back by ten o'clock at the latest.她最晚应该在10点前回来。
