—How unhappy your roommate looks!

—Yes, but he's not willing to tell me what it is ________ is troubling him.

A．what

B．which

C．as

D．that

冠心病稳定型心绞痛合并高血压首选（）

A.β受体阻滞剂 

B.利尿剂 

C.a受体阻滞剂 

D.血管紧张素II受体阻滞剂 

E.钙通道阻滞剂