问题补充:
I didn’t know .
A. when did the plane take off
B. when the plane took off
C. when the plane takes off
D. when does the plane take off
答案:
A. when did the plane take off
(答案→)B. when the plane took off
C. when the plane takes off
D. when does the plane take off
解析:特殊疑问词作宾语从句,将特此作为连接词,后接陈述句语序。故选B