成品胶二级品门尼值要求应为（）。
A.45±5
B.45±7
C.45±2
参考答案：B
—Did you have any difficulty catching yesterday’s lecture?
—No. The professor spoke very clearly to make his speech easy _____.
A．understood
B．understanding
C．to be understood
D．to understand
计算题：某煤气管道，当压力为500Pa时，测气流量为40m3/秒，在煤气管道完全不变的情况下，当压力增加到1000Pa时，煤气流量应变为多少？
