孟赛尔系统颜色的标准表示方法为（）。H-色调 V-明度 C-彩度
A.H/VC
B.HC/V
C.VC/H
D.HV/C
参考答案：D
It is predicted that a comet will probably hit the earth in about 10 years and scientists all over
the world are thinking about possible ways to ________it from happening. Which of the following
is not OK? [ ]
A. protect
B. stop
C. keep
D. prevent
以下哪项不是生殖道感染的途径（）。
A.内源性感染
B.性传播感染
C.医源性感染
D.血液途径传播
