Gun control is the subject ________ Americans have argued for a long time.

A．which

B．with which

C．about which

D．of which

资本总公式的矛盾是

A．商品流通与货币流通的矛盾

B．生产过程和流通过程的矛盾

C．价值增值与价值规律客观要求的矛盾

D．劳动与劳动力的矛盾