He knew the problem was serious and promised to look into it he reached office.A. at tha

问题补充：

He knew the problem was serious and promised to look into it he reached office.

A. at that moment

B. for that moment

C. immediately

D. soon

答案：

A. at that moment

B. for that moment

(答案→)C. immediately

D. soon

解析：immediately = as soon as