若要探究“种子的萌发是否需要适量的水分？”，你认为该实验的变量是

A．水分

B．空气

C．温度

D．阳光

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