如图，△AOB中，∠AOB=90°，AO=2，BO=4，△AOB绕顶点O逆时针旋转到△A′OB′处，此时线段A′B′与BO的交点E为BO的中点，则线段B′E的长度为____ 

短文填空，根据短文内容和首字母提示，把文中所缺词语补充出来，使短文完整、正确、通顺。（每空限填一词。）

     Nowadays, you can see many people busy on their smartphones(智能手机) if you look a____ Smartphones make our lives easier. But have you ever t ____  about what they mean to your eyes?

    Staring(盯) at smartphones for long time gives you dry eyes and even causes a disease c____ glaucoma(青光眼).

While you're probably not going to stop using your smartphone, there are a few things you can do to protect your eyes. Hold your phone at least 30 cm away from your eyes when using it. Take a break every h____  and try the following: look at something at least five meters away from you and then focus on the tip of your nose. Repeat this s____ times. It should reduce(减少) the discomfort in your eyes.

为吸引游客，实行团体入住五折优惠措施，一个50人的旅游团优惠期间到该酒店入住，住了一些三人普通间和双人普通间客房，若每间客房正好住满，且一天共花去住宿费1510元，则旅游团住了三人普通间和双人普通间客房多少间？

下列有关巴黎公社革命措施的表述，不正确的是（   ）