当平均动脉压（MAP）降至60mmHg时，肾小球滤过率（GFR）下降（）
A.50%
B.60%
C.70%
D.80%
E.90%
参考答案：A
若一元二次方程的x2-2x-3599=0两根为a，b，且a＞b，则2a-b的值为______．
32. 一You were brave enough to raise objections at the meeting．
一 Well, now I regret_________ that．
A．to do
B．to be doing
C．to have done
D．having done
