使用含铅汽油能使空气中的铅含量增多，引起铅中毒。下列说法中，正确的是（） A．铅

Last night it snowed heavy. When Susan and I got up in this morning, we found the whole garden was covered with thick snow. So we decided clear the path. We got two spades but began our work at once. We both worked so hard that the path was clear soon. Seen this, our father felt very surprising. He smiled happily at us, telling us that we have done a good job and that he was proud for us. Finally Father gave us some pocket money as a reward for the Spring Festival. Susan and I was happy because we had all got the money through labor.

操作剪床，当踏下脚踏开关后，在操作机构的作用下，上、下剪刀进行剪切。

对于寿命期不同的多个方案比选，选用（）指标合适。

A、投资收益率

B、内部收益率

C、动态投资回收期

D、净年值

下列不是容积式流量计的是（）。

A.椭圆齿轮流量计

B.孔板流量计

C.活塞式流量计

D.圆盘式流量计