方程a-x=logax(a＞0且a≠1)的解的个数为（ ）。
1
-Where has all the time gone? I can still remember the day when I first came to this school, but now I am about to leave.
-_______.
A．That makes two of us
B．One is never too old to learn
C．I don't have a clue
D．The grass is always greener on the other side of the fence
DCS系统由哪几种不同的通讯网络组成？
