Nowadays many people set up their own Blogs on the Internet, _______ they can express themselves freely or communicate with others.

A．which

B．to which

C．that

D．where

关于机组氧气面罩的说法正确的是（）

A.可以选择供应稀释氧气

B.可以选择供应纯氧

C.持续供应稀释的氧气或纯氧

D.氧气面罩的束带要先充气才方便带上