商品价格时常在变，又不会有巨大变化，商品价格总是围绕价值上下波动，原因是

①价格受供求关系影响  ②价格影响供求关系

③价格由价值决定      ④价格决定价值

A．①②

B．③④

C．①③

D．②③

It hasn't been made clear     ________  the new underground line is to be open to traffic.

A．when

B．that

C．what

D．where