645　be supposed to do通常表示两种含义

① 表示“应该，推测，预定”，与be expected相近。

He is supposed to arrive at eight. I wonder why he is late. 他应该8点钟到的，不知道为什么迟到了。

When the bell rings，the students are supposed to hand in their test papers. 铃一响，学生们就该交考卷了。

② 表示“必须，有义务做”，与ought to相近。

Soldiers are supposed to keep military discipline. 军人必须遵守军纪。

We are not supposed to solve all of these problems. 我们没有义务解决所有这些问题。