若直线y=2x-4与两坐标轴所围成的三角形面积是（ ）。
4
They didn't watch TV _______ they finished their homework. [ ]
A. when
B. as
C. while
D. until
β受体阻断药的禁忌症是（）
A．稳定型心绞痛
B．重度房室传导阻滞
C．窦性心动过速
D．高血压病
