使舵力增大的因素包括：（）.Ⅰ伴流Ⅱ排出流Ⅲ失速现象Ⅳ空泡现象
A.Ⅰ～Ⅳ
B.Ⅰ～Ⅲ
C.Ⅱ
D.Ⅰ、Ⅲ、Ⅳ
参考答案：C
单项选择。
— Where are the runners?
— Over there. They ______ warming-up exercises. [ ]
A. is doing
B. do
C. are doing
D. does
紫外线杀菌的最适波长为（）
A.242nm
B.255nm
C.265nm
D.286nm
E.以上都不对
