题干

昆虫观察盒的盒盖是一个凸透镜(如图所示),盒盖到盒底的距离为10cm,利用凸透镜能成正立、放大像的原理可以方便地观察小昆虫.在一次实验中,小明不小心把盒盖上的凸透镜打碎了.为了修好观察盒,老师分别给他提供了焦距为4cm、8cm、10cm和12cm的凸透镜各一个,他应该选择 (  )

A:焦距为4cm的凸透镜

B:焦距为8cm的凸透镜

C:焦距为10cm的凸透镜

D:焦距为12cm的凸透镜

上一题 下一题 0.0难度 选择题 更新时间:2019-11-04 09:05:51

答案(点此获取答案解析)

D

同类题4

阅读下列短文,从每小题所给的A、B、C、D四个选项中选出一个最佳选项。

Going Green

    Green is no longer just a color. It is a new way of thinking about the world and a way of living your life. It's catching on all over the world. More and more people decide to “go green” because they know that we only have one planet to live on. We won't be able to live on it much longer if we keep wasting energy, and destroying(破坏) our home with air, land, and water pollution.

    “Green Living” means:

    Understanding that your choices affect(影响) not just you, but everybody everywhere.

    Understanding that your choices affect not just today, but the future.

    Understanding that when we talk about “saving the planet” or “saving the environment,” we are actually talking about saving ourselves!

    You may be thinking: “Hey, I'm just one person, on a planet with billions. I can't really make a difference.” Well, have you ever seen a group of people do “the wave(波浪)”? It always starts off with one or two people, jumping up and down like crazy. Soon thousands of people are joining in. “Going green” is just like that. It starts with small, simple actions. It can soon build into a wave that will change the whole planet and lead us all to healthier, happier lives.

    Many students have already shared with us their efforts to help the environment:

    Gabrielle, 12, writes, “I have helped my community plant a garden and I ride my bike or skateboard to school.”

    Kaitlyn, 10, says, “Lots of paper towels are thrown away, so I use a reusable cloth towel to dry my hands instead.”

    “I always recycle(重复利用)” says Natalie, 13. “You can call me a recycler! I always look at the bottom of things. I want to see whether they have the little sign that tells you it can be recycled. So I almost recycle everything!”

    Now it's your turn to think about how you can “go green”. Make important choices and take actions to improve the environment right around you and the health of the whole world.