Is she Chineseor Japanese?

She can't beJapanese. She must be Chinese.

Is it the 24th orthe 25th today?

It can’t be the24th. It must be the 25th.

Are they watchingvideos or playing games?

They can't bewatching videos. They must be playing games.

Is the program the1st one or 2nd in today's show?

It can't be the 1st.It must be the 2nd.

Is she 35 or 40?

She can't be 40. Shemust be 35.

Is she making up orhaving a shower?

She can’t be havinga shower. She must be making up.

Is he a ChineseTeacher or English Teacher?

He can't be anEnglish teacher. He must be a Chinese teacher.

表达过去的判断

Was he a doctor ordentist?

He can't have been adoctor. He must have been a dentist.

When youwere waiting, was she making up or having a shower?

She can'thave been making up. She must have been having a shower. 

Was it the24th or the 25th yesterday?

It can'thave been the 24th. It must have been the 25th.

When shebecame the CEO, was she 35 or 40?

She can'thave been 40. she must have been 35.

Did shefinish ( reading) the 1st part or the 2nd part?

She can'thave finished the 2nd part. She must have finished the 1st part.