计算：（2x-1）（2x+1）-（2x-3）2。
解：原式=4x2-1-（4x2-6x+9）
=4x2-1-4x2+6x-9
=6x-10。
The fact that fun is not equal to happiness may be the opposite of ______ many people actually understand.
A．why
B．that
C．which
D．what
特种服务号码的首位是1，号长是四位。
