cDNA是指（）

A.在体外经反转录合成的与RNA互补的DNA

B.在体外经反转录合成的与DNA互补的DNA

C.在体内经反转录合成的与RNA互补的RNA

D.在体外经反转录合成的与RNA互补的RNA

E.在体内经反转录合成的与RNA互补的DNA

They enjoyed fresh watermelon last fall because they______ watermelon seeds in the spring.

A．were planting

B．would plant

C．have planted

D．had planted