我国的人口问题不仅表现为人口基数大，新增人口多，还表现在                   等方面。[ ]

①人口素质偏低②农村人口多③人口的老龄化速度加快④人口的分布不平衡⑤男女性别比失衡

A．①②③

B．②③⑤

C．①②③④⑤

D．②③④

Each hose used for transferring vapors must（）.

A.have a design burst pressure of at least 25 psig

B.be capable of withstanding at least 2.0 psi vacuum without collapsing or constricting

C.be electrically continuous with a maximum resistance of ten thousand ohms

D.All of the above