题干

下列现象中属于白光色散的是(  )

A:太阳光经过棱镜后,分解成各种颜色的光

B:红、绿、蓝三种色光合成电视画面的颜色

C:红、绿、蓝三色光按一定比例混合成白光

D:红、蓝、黄三色颜料按一定比例混合成黑色

上一题 下一题 0.0难度 选择题 更新时间:2019-04-11 08:09:32

答案(点此获取答案解析)

A

同类题3

任务型阅读

You Can Fly More Frequently

    When traveling, airfare can take up a large part of your travel budget. What if you could fly practically for free? If it were possible, then you would probably travel more, right?____ While it may seem like a lot of work to accumulate miles, it's pretty easy when you know how.

    Sign up for mileage (里程) programs. You can't gain miles if you don't sign up.____ Pick one or two airlines that you use most often and try to bring all your points into those programs by flying with them.

    Buy gifts and have dinner out. Most mileage programs have a business list where you can register several credit or debit cards and then earn miles for each purchase you make through their participating shops or meal you have at restaurant partners.____so why not make it count toward future travel?

    Use your credit card. Look for a card that gives you rewards. There are a ton of credit card companies that offer mileage cards that give you miles for each dollar you spend. Use it for bills, groceries, gas and anything else you would normally use your bank account for and then pay it off at the end of the month.____

    Rent a car. Whenever you rent a car, you have the choice to include your frequent flyer member number.____ but it can be more beneficial to pay less than a dollar a day to earn one or more miles per dollar spent on your rental.

A. Some will charge a fee

B. With frequent flyer programs, you can

C. You're probably doing these things anyway

D. It's an easy way to accumulate miles and can add up really fast

E. In fact, you can get a free plane ticket just focusing on certain ones

F. Join frequent flyer programs, so you can start accumulating those miles

G. There are plenty of ways to earn money just by doing things you're already doing

同类题5

阅读下文,回答问题

哈勃,太空中的千里眼

    ①古往今来,人们用肉眼观察灿烂的星空,很多发现难免显得粗糙,甚至只是一些臆想。当伽利略等人将望远镜对准了茫茫太空后,人们才逐渐发现了太空的更多奥秘。

    ②在实践中,人们发现用地面的望远镜观测太空,存在两个缺陷:一是地球大气层会吸收红外线和紫外线,二是大气湍流导致地面光学望远镜的角分辨率很难优于1弧秒。1946年,美国天文物理学家斯皮策提出,在太空中安装一台望远镜将突破上述限制。

    ③1990年,这一设想终成现实。美国“发现”号航天飞机将哈勃望远镜送入了太空。然而,哈勃探索宇宙奥秘的征途并非一帆风顺。升空伊始,哈勃就被发现患了“近视眼”,不能辨别140亿光年以外的物体。此后哈勃的陀螺仪、太阳能电池板、影像摄谱仪、绝热毯、冷却剂等都出现过故障,历经五次“手术”才恢复正常。然而哈勃望远镜面临的挑战,也激励着人们推动科研设备及制造技术的革新。每一次维修都让哈勃能够看得更清晰、更遥远。2009年第五次维修后,哈勃望远镜的观测能力已是最初设计的100倍。

    ④哈勃望远镜得到的数据引发了天文学的革命:它确定了宇宙历史为137亿年左右,证实超大质量黑洞处于大多数星系的中心,它让科学家更好地理解恒星和行星的形成,并探测到太阳系外存在有机物。20年来,科学家利用哈勃望远镜的数据发表了7500多篇论文,使之成为历史上最有科学价值的仪器。美国资深宇航员马斯格雷夫说,哈勃望远镜的价值不仅在于它是一台强大的机器,而且在于它把宇宙论、神学、哲学和天文学贯穿了起来。它是人类的一面镜子,让人类自省:这是一个什么样的宇宙?我们处在什么位置?我们是谁,我们该如何作为?

    ⑤虽然哈勃望远镜将于2014年退休,詹姆斯·韦伯太空望远镜将接过它的接力棒,将人类对深层太空的探索继续下去。