__________ the housing price, several measures have been adopted in the last two years.

A．Lowering

B．Having lowered

C．To lower

D．To have lowered

关于电磁波频率的说法，正确的是（）。

A.其代号为s

B.其计量单位为ms

C.其计量单位为mA

D.是电磁波的振荡的次数

E.是单位时间内电磁波波动的次数