Not only , but I learned some knowledge.
A. did I help other people
B. do I helped other people
C. I helped other people
D. helping other people
网友回答
(答案→)A. did I help other people
B. do I helped other people
C. I helped other people
D. helping other people
解析：not only…but （also）是“不但……而且”的意思。当其放在开头时，应该用倒装结构。故应排除CD；根据后句的时态可知，本句也应该用过去时。所以本题选A。