热力管道安装应设有坡度，汽水同向流动的蒸汽管道坡度一般为（）。
A.0．002
B.0．003
C.0．004
D.0．005
参考答案：B
My friend told me it would be months _________ his family settled down in that city.
A．after
B．since
C．before
D．when
OTDR测试中，脉宽设置越长，动态测量范围（）
A.越少
B.越小
C.越大
D.越长
