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

运营商级NAT（NAT444）的主要功能是（）。

A.提供安全保障

B.提供IPv4到IPv4的地址转换

C.提供IPv4到IPv6的协议转换

D.提供IPv6到IPv6的转换