People laugh at jokes, but seldom about how they work.
A. they think
B. think they
C. they do think
D. do they think
网友回答
A. they think
B. think they
C. they do think
(答案→)D. do they think
解析：句意：人们觉得笑话好笑，但是很少有人想这些笑话是怎么起作用的。Seldom“很少”是否定词，放在句首的时候，句子用部分倒装，助动词do放在主语前面，所以选D。