已知x²﹣x﹣6=0，求$\frac{x^2}{x^3+x^2+36}$的值．

集合A={1，2}共有____ 子集．

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.

下列说法中正确的是（   ）