（ ）finishing his homework, he went to play basketball with his classmates.
A、
In
B、
Upon
C、
As soon as
D、
At
【正确答案】：B
【题目解析】：
A. In +时间段，表示多长时间以后，用在将来时态中；B. Upon +doing sth. 相当于As soon as+从句，表示一……就……；C. As soon as+从句, 一……就…… 后接从句；D. At+时间点，表示在几点钟。由题意可知选B正确。
句意：他一完成家庭作业，就和同学一起打篮球了。