出现黑便表明出血量在多少以上
A．50～70mlB．70～90mlC．80～100mlD．90～120mlE．120ml以上
参考答案：A
由于中放管结电容的存在，中频放大器输出阻抗与（）有关。
Many people can't learn any lessons from the mistakes they've made _____ they get hurt somehow.
A．whether
B．unless
C．if
D．as
