关于合力的下述说法中正确的是[ ]

A．合力的性质与原来分力性质相同

B．合力与原来的分力间的关系是等效替代关系

C．合力总比分力大

D．合力总比一个分力大，比另一个分力小

I'm tired out. I ______ all afternoon and I don't seem to have finished anything.

A. shopped


B. have shopped
C. had shopped


D. have been shopping