下列关于指数基金的说法，正确的有( )。

A．收益随证券价格指数上下波动

B．始终保持即期的市场平均收益水平

C．可以完全消除投资组合的非系统风险

D．可以消除一部分投资组合的非系统风险

An inflation life raft is thrown into the water from a sinking vessel, what occurs automatically after the painter trips the C0₂ bottles to inflate the raft?（）.

A.The sea anchor deploys

B.The floor inflates

C.If upside down, the craft rights itself

D.The painter detaches from the raft