had to 还是 must have been?

精讲课笔记随视频锁定

右侧笔记支持独立滚动。边听名师连读拆解，边对照右侧的语法事实与统计数据笔记。

had to ... 不得不^(过去式)	must have been ... ^{过去肯定表推测}
I lost my pen so I had to buy a new one. ^不能推测 He forgot his case so he had to return home. ^不能推测	He didn't come to work yesterday. He must have been ill. ^非动词 He didn't come to the office this morning. He must have stayed at home. ^{动词完成时态} I don't think she was Austrian. She must have been German. ^非动词 She didn't hear the phone. She must have been sleeping. ^动词