The speaker several other subjects in the course of his talk but mostly kept himself to the main topic.
A. held on
B. worked out
C. touched on
D. kept out of
网友回答
A. held on
B. worked out
(答案→)C. touched on
D. kept out of
解析： touch on简单谈到，由抠门的关键词：but mostly kept himself to the main topic.
可知答案。