I have to be in bed by ten o'clock.

by ten o'clock------在10：00以前 === no later than / before 10:00
at 10:00 ------在10：00整
have to be in bed ------必须上床睡觉 （肯定句的句型）have to be in bed，为什么have to 后面要加be ，这是个怎样的句子结构你好again. have to 是情态动词，它不能表达谓语动词的完整意义，所以在have to 的後面必须加上真正动词/ 行为动词，它们一起构成复合谓语。be in bed 是一个动词短语------上床睡觉。我还以为是 have to be ,加 in bed 呢是have to + be in bed. 祝你愉快。