It's nine o'clock in the morning.The teacher promosed that they should get_at onceA starting B.start C to start D.started答案及选择的原因 最好能够提供相关的语法知识.

问题描述:

It's nine o'clock in the morning.The teacher promosed that they should get_at once
A starting B.start C to start D.started
答案及选择的原因
最好能够提供相关的语法知识.