y=（sinx﹣cosx）²﹣1是最小正周期为  　  [     ]

A．2π的偶函数

B．2π的奇函数

C．π的偶函数

D．π的奇函数

Too high house prices can be brought under control，_______  the government introduces a series

of regulatory policies．

A．even if

B．as if

C．so that

D．as long as