问题 选择题

据报道,“毒淀粉”是在淀粉中添加了对人体有害的马来酸(C4H4O4).马来酸是无色晶体,能溶于水.下列关于马来酸的说法中正确的是(  )

A.马来酸属于氧化物

B.马来酸中氧元素的质量分数最大

C.马来酸中碳、氢、氧三种元素的质量比为1:1:1

D.5%的马来酸溶液中氧元素的质量分数为2.76%

答案

A、马来酸是由碳、氢、氧三种元素组成的,不属于氧化物,故选项说法错误.

B、马来酸中碳原子的相对原子质量之和为12×4=48,氢原子的相对原子质量之和为1×4=4,氧原子的相对原子质量之和为16×4=64,氧元素的相对原子质量之和最大,则氧元素的质量分数最大,故选项说法正确.

C、马来酸中碳、氢、氧三种元素的质量比为(12×4):(1×4):(16×4)≠1:1:1,故选项说法错误.

D、5%的马来酸溶液中含有90%的水,水中氧元素的质量分数为

16
18
×100%≈88.9%,马来酸溶液的水中氧元素的质量分数为90%×88.9%=80%,马来酸中还含有氧元素,故5%的马来酸溶液中氧元素的质量分数大于80%,故选项说法错误.

故选:B.

阅读理解

B.

My secret for staying young is simple. Put all attention to the part of you---your brain and keep it young and growing. Keep your mind awake and you’ll stay young all over. These are exciting time. Take an interest in the world around you, and stick to(坚持) learning at least one new thing every day.

No matter how old you are, it’s not too late to make your life more interesting. I know a housewife with no knowledge before who made herself into a famous industrial engineer(工业工程师).I know a retired(退休) electrical engineer who has became a highly-paid ceramin (陶器的) artist.

Get over the idea that you are ever too old to go back to school. I know a man who entered a medical college at 70.He got his degree with honor and became a doctor. Another man went to law school at 71 and now is an active lawyer(律师).Staying young is easy for those, old or young, who live in the future. You can do it if you care enough to try. Keep you mind awake and active: that’s the only elixir(万验灵丹)

41.The statement that brain to people of all ages, remains young and growing is_____.

A.impossible                               B.a scientific fact(科学事实)

C.supposed(或许) to be true        D.a wrong conclusion( 错误结论)

42.It is wrong to______.

think oneself too old to go back to school  B.keep one’s mind awake

try to stay young                      D.get one’s degree with honors

43.The passage tells that the man who entered college at 70 became_____.

A.an active lawyer                       B.an electrical engineer

C.a famous doctor                       D.a highly-paid ceramic artist

44.The only youth elixir is______.

to go back to school                     B.not to think about one’s age

to live in the future                  D.to keep one’s mind awake and active

45.According to the writer,you should_____learning at least one new thing every day.

A.take care of        B.start            C.begin          D.keep on

判断题