核算管道应力的目的是了解该管道应力是否小于或等于管子的屈服极限的（）倍。
A、0.5
B、0.7
C、0.9
D、1.0
参考答案：C
My English teacher has______ rich experience in teaching and we all think she is ______ experienced teacher.
A．不填; an
B．a; an
C．不填; the
D．a;the
什么是发现抽样？如何抽样？
