Question

--How long have you been in the school? --By the end of 2012,i _English for exactly 30 years and

i __in 5years.
A.willl have taught;will retire
B.have been teaching; am to retire
答案是b 但我想不通a 不是挺对的么

Answer 1

By the end of 2012,i _English for exactly 30 years and i __in 5years.

by开头，表示“到……（某时间）”且其间一直持续，所以用been teaching表示延续性状态

am to retire则表示到某时间注定会发生的事件

，A其实口语中可能这么用，但这种考察严格语法的单选题要选出最适当的答案