聚乙烯分为（）。
A.高压聚乙烯
B.中压聚乙烯
C.聚氯乙烯
D.低压聚乙烯
E.聚氯乙烯
参考答案：A, B, D
Did you see Xiao Li at the party? No, ___ by the time I arrived.
A．she had left
B．she has left
C．she was left
D．she must left
径向防砂设计的原理是什么？
