is to的意思

I am to do sth ,,,,,
be ( is , am , are , was , were ) + infinitive 不定式

1 ) 傳達指示或命令 :
No one * is to leave this building ,,,, 任何人不得離開 ,,,,
He * is to stay here ,,,, 他必須逗留 ,,,,,
We * are to wait ,,,,, 我們必須等 ,,,,,

2 ) 用於間接引句 , 意為 " 應該 "
' Where * shall I put it ? ' he asked .
He asked where he * was to put it .

3 ) 表示計劃安排 :
She * is to be married next month . 她預定於下個月結婚 .
He * is to start in a week' s time . 他預定於一週後出發 .

4 ) was / were + infinitive 表示一種意料不到的情況 :
They said goodbye , little knowing that they * were never to meet again .
,,,,,, 沒想到竟然再也不能相見 ,

I am to do sth = I should do sth

am to/is to = present tense
was to = past tense