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问题 选择题

将一定量的乙醇（C2H6O）和氧气置于一个密闭的容器中引燃，测得反应前后各物质的质量如表所示（　　）

物质乙醇氧气水二氧化碳X
反应前质量/g4.68.0000
反应后质量/g005.44.4a

A．表中a的值为2.6

B．X一定是该反应的催化剂

C．X可能含有氢元素

D．X一定含有碳元素

答案

A、由表中数据分析可知，反应前后，乙醇的质量减少了4.6g，故乙醇是反应物，参加反应的乙醇的质量为4.6g；同理可以确定氧气是反应物，参加反应的氧气的质量为8.0g；水是生成物，生成的水的质量为5.4g；生成二氧化碳的质量为4.4g；由质量守恒定律，X应是生成物，且生成的X的质量为4.6g+8.0g-5.4g-4.4g=2.8g，故表中a的值为0g+2.8g=2.8g；故选项说法错误．

B、由A选项分析可知，X的质量增加，故一定不是该反应的催化剂，故选项说法错误．

C、根据反应前后元素质量不变，反应物乙醇中含氢元素的质量为4.6g×

1×6
12×2+1×6+16
×100%=0.6g，生成物水中含氢元素的质量为5.4g×
1×2
1×2+16
×100%=0.6g，氢元素的质量相等，故X中不含氢元素；故选项说法错误．

D、根据反应前后元素质量不变，反应物乙醇中含碳元素的质量为4.6g×

12×2
12×2+1×6+16
×100%=2.4g，生成物二氧化碳中含碳元素的质量为4.4g×
12
44
×100%=1.2g，X一定含有碳元素．

故选：D．

单项选择题

"In the long run," as John Maynard Keynes observed, "we are all dead. " True. But can the (1) run be elongated in a way that makes the long run (2) And if so, how, and at what cost People have dreamt of (3) since time immemorial. They have sought it since the first alchemist put an elixir of (4) on the same shopping list as a way to turn lead into gold. They have (5) about it in fiction, from Rider Haggard’s "She" to Frank Herbert’s "Dune". And now, with the growth of (6) knowledge that has marked the past few decades, a few researchers believe it might be within (7) .

To think about the question, it is important to understand why organisms-people (8) -age in the first place. People are like machines: they (9) That much is obvious. However, a machine can always be (10) A good mechanic with a stock of spare parts can keep it going (11) . Eventually, no part of the (12) may remain, but it still carries on, like Lincoln’s famous axe that had three new handles and two new blade.

The question, of course, is whether the machine is worth (13) . It is here that people and nature (14) . Or, to put it slightly (15) , two bits of nature disagree with each other. From the individual’s point of view, (16) is an imperative. You cannot reproduce unless you are alive. A fear of death is a sensible evolved response and, since (17) is a sure way of dying, it is no surprise that people want to stop it in its tracks. Moreover, even the appearance of ageing can be (18) . It (19) the range of potential sexual partners who find you attractive-since it is a sign that you are not going to be (20) all that long to help bring up baby-and thus, again, curbs your reproduction.

1（）

A.short

B.long

C.shorter

D.longer
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判断题

桩基础处理，按照受力的不同可分为支承桩和摩擦桩。（）
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