牙石

气相色谱分离的基本原理是什么

计算化肥尿素〔CO（NH₂）₂〕的式量．

Internet的网络管理是使用的下面的协议。

A．SMTP

B．FIP

C．SNMP

D．TELNET

实验室既可用浓盐酸与MnO₂在加热时反应制备Cl₂，也可用KMnO₄与浓盐酸在常温下反应制备Cl₂，下列有关说法中不正确的是(  )

A．由题目信息知：KMnO₄的氧化性比MnO₂的强

B．制备氯气的整个实验过程中，只需要使用氧化剂与还原剂

C．用排气法收集不需要利用其他试剂就能确定集气瓶中已收集满气体

D．用足量MnO₂与含有4 mol HCl的浓盐酸在加热条件下反应，得到Cl₂的物质的量小于1 mol

Recently, I flew to Las Vegas to attend a meeting. As we were about to arrive, the pilot announced with apology that there would be a slight (16) before setting down. High desert winds had (17) the airport to close all but one runway. He said that we would be (18) the city for a few minutes waiting to (19) . We were also told to remain in our seats meanwhile with our seat belts fastened (20) there might be a few bumps(颠簸). Well, that few minutes turned into about four-five minutes, including a ride that would make a roller coaster(过山车) (21) by comparison. The movement was so fierce that several passengers felt (22) and had to use airsickness bags. As you might guess, that’ s not a good thing to have happen in a(n) (23) space because it only (24) to increase the discomfort of the situation.

About twenty minutes into the adventure, the entire airplane became very (25) There was now a sense of anxiety and fear that could be (26) noticed. Every passenger simply held on for dear life …except one. A (27) was having a good time！ With each bump of the (28) , he would let out a giggle (咯咯地笑)of delight. As I observed this, I (29) that he didn’t know he was supposed to be afraid and worried about his (30) . He neither thought about the past nor about the future. Those are what we gown--ups have learned from (31) . He was (32) the ride because he had not yet been taught to fear it. Having understood this, I took a deep breath and (33) back into my seat, pretending I was (34) on a roller coaster. I smiled for the rest of the flight. I even (35) to giggle once or twice, much to the chagrin(随恼) of the man sitting next to me holding the airsickness bag.

（17）（）

A．forced

B．warned

C．swept

D．reminded