--- do you usually read English in the morning?
---About half an hour.
A. When
B. What time
C. How many
D. How long
网友回答
A. When
B. What time
C. How many
(答案→)D. How long
解析：疑问词辨析。When什么时候；What time几点钟；How many多少个；How long多长。根据答语About half an hour大约半个小时，可知上文提问时间长短，故用how long来提问。选D。