题干

三聚氰胺(结构式如图所示)是一种重要的化工原料,可用于阻燃剂、水泥减水剂和高分子合成等领域。一些不法分子却往牛奶中加入三聚氰胺,以提高奶制品的含氮量。下列说法正确的是

   

A:三聚氰胺是一种蛋白质

B:三聚氰胺是高分子化合物

C:三聚氰胺分子中含有碳碳双键

D:三聚氰胺的分子式为C3H6N6

上一题 下一题 0.0难度 选择题 更新时间:2012-01-03 01:06:55

答案(点此获取答案解析)

D

同类题4

阅读下面短文,从短文后各题所给四个选项(A、B、C和D)中,选出可以填入空白处的最佳选项,并在答题卡上将该项涂黑

    Many people think that babysitting is one of the1jobs for young people. They imagine a teenager putting a few well-behaved children to bed and then continuing to watch television until the parents return home to hand over some money. Well, I can tell you how2that thought is.

    I now work all3on Wednesdays for a Ukrainian family with three young boys. In the early morning, I go there to 4the older two while their mother does her jobs or takes care of her six-month-old baby. However, I am also there to5their English by teaching them songs and games in my native language.

    Now, four months later, I get home at the end of the day6exhausted!Babysitting is not a job for the7or the weak. I expected8children who would behave well and listen to me all the time. 9,I don't think those kind of children exist at all. While my two boys are usually polite and calm, they are10children and also like to fight, scream and lose their temper for no real11. I often have no idea why they cry together.

    Being a babysitter requires you to play a hundred different12throughout the day. I have to be a friend when I play with the boys, but their 13when I tell them to do something. When they hurt themselves, I have to be their14, and when they fight over15 things like sharing their crayons(彩笔),I have to be a negotiator(调停者)。 When lunchtime rolls around, I am a(n) 16to prepare the meal and then a maid as I clean up after lunch. Finally, in English, if someone is very17, we say they have the “Patience of God”. I think I embody(体现) this 18sometimes!

    Despite the19involved in my job, I usually do enjoy it. Working with children is so tiring that I always feel20after leaving them with their parents at the end of the day!