电机车车闸接触面积小于（），会影响制动效果，造成制动距离超限。
A.30%
B.40%
C.50%
D.60%
参考答案：D
Even when I am able to get in touch with the manager and tell him your request, I cannot __ he will reply.
A．stress
B．appeal
C．inform
D．guarantee
在紫外分光光度法中，供试品溶液的浓度应使吸收度的范围在
A．0.1～0.3
B．0.3～0.5
C．0.3～0.7
D．0.5～0.9
E．0.1～0.9
