The teacher asked the students .A. what they were doing at that momentB. what were they do

问题补充：

The teacher asked the students .

A. what they were doing at that moment

B. what were they doing at that moment

C. how are they doing at that moment

D. what they are doing at that moment

答案：

(答案→)A. what they were doing at that moment

B. what were they doing at that moment

C. how are they doing at that moment

D. what they are doing at that moment

解析：英语宾语从句中一般为陈述语序。根据从句中的时间状语at that moment那时，可知从句描述的是过去某时发生的动作，故用一般过去时态。故选A。