Siberian Tigers ________ and killed at such a speed that they will disappear from the earth in the near future.

A．hunted

B．are hunted

C．are being hunted

D．had been hunted

供暖系统按照热媒的不同可以分为（）。

A.热水供暖系统

B.蒸汽供暖系统

C.太阳能采暖系统

D.热风采暖系统