题干

某外控型食品保鲜剂以淀粉、二氧化硅(SiO2)为载体,吸附酒精制作而成.保鲜原理是酒精缓慢挥发,某食品周围形成一定浓度的气体保护层.下列说法不正确的是(   )

A:SiO2中硅元素化合价为+4

B:该保鲜剂不能与明火接触

C:起保鲜作用的物质是酒精

D:酒精挥发时分子体积变大

上一题 下一题 0.0难度 选择题 更新时间:2019-07-24 10:46:24

答案(点此获取答案解析)

D

同类题1

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

    Teachers selected from each district school for the Teacher of the Year competition were recognized.The competition's winner will be1in the spring.All those model teachers got me to think about some of my teachers through the years, and how they2me.

    My college adviser, J.C.Casey, had a big3on my life.She was a teacher and friend.She4me to consider journalism as a career.My high school math teacher,Kathy Cloud,took the time to5math to me in a way I could    6understand.I'd struggled with math until I got in Cloud's classes.She gave me the7to realize I could do it.

    My first-grade teacher, Darlene Dryden, held me back. Now, most people wouldn't8the teacher that kept them back a grade fondly, but Dryden has always been my9teacher.I was the youngest person in my class and very shy. She thought I10another year to mature before moving on to second11.She didn't make me feel12for having to repeat the grade.Instead,he made me feel13.I think I was her favorite, too.

    My senior year of high school, right before14,I wrote Dryden a note letting her know that I'd become a good student and was going to15and that she'd had a16in that.

    The Norman teachers17Wednesday are just a few of the many who are in the classrooms every day making 18in their students' lives.They may not even know the19impact(影响)they're having.I know it's not an20 job, but teachers, just remember that you're a Mrs.Dryden to somebody.