证明假设最可靠的方法为
A．回顾性调查
B．现况调查
C．动物实验
D．抽样调查
E．实验流行病学
参考答案：E
Mr. Brown is _____ a teacher to us; we look on him as our friend.
A．not more than
B．no more than
C．more than
D．less than
激光工离岗前为什么要关好气瓶伐门？
