若按调速系统是否存在稳态偏差来分类，可将调速系统分为（）系统和（）系统。
参考答案：有静差；无静差
It is said that the number of doctors invited to the meeting _____100, but a number of them _____ absent for different reasons.
A．is; were
B．is; was
C．are; were
D．are; was
低位肠梗阻呕吐的特点（）
A.呕吐物为血性
B.呕吐早、频繁
C.呕吐出现晚、呕吐物带粪臭味
D.呕吐物为带酸臭味的宿食
E.呕吐呈溢出性
