With many major economic problems________ to be solved, there is no point predicting the growth rate of this year now.

A．remaining

B．remained

C．have remained

D．having remained

下列物质不能使血管平滑肌舒张的是（）

A.缓激肽

B.血栓素

C.局部代谢产物

D.前列环素

E.组胺