导管使用前应进行试拼和试压，试压压力宜为孔底静水压力的（）倍。
A、1
B、1.5
C、2
参考答案：B
中国居民平衡膳食宝塔的第四层是（）
A.肉、禽、鱼、蛋类
B.蔬菜和水果类
C.乳类和豆类
D.油脂和盐
E.谷类和薯类
The radiotelegraph alarm signal is（）.
A.SOS sent three times
B.ten one-second dashes with a four-second interval between them
C.twelve four-second dashes with a one-second interval between them
D.twelve one-second dashes with a short interval between them
