下列关于误码率说法错误的是______。

A．误码率是二进制码元被传错的概率

B．误码率越低越好

C．误码率可以衡量系统的可靠性

D．必须折合成二进制码元来计算

I didn't understand ______ so I raised my hand to ask. [ ]

A.what my teacher says

B.what does my teacher say

C.what my teacher said

D.what did my teacher say