Gun control is a subject Americans have argued for a long time,
A. of which
B. with which
C. into which
D. about which
网友回答
A. of which
B. with which
C. into which
(答案→)D. about which
解析：考查定语从句：介词+which引导的定语从句修饰subject，从句中argue是不及物动词，argue about sth“争论某事”选D。