在式子x²+$\frac{1}{7}$，﹣1，x²﹣3x，$\frac{5}{x}$，x²+$\frac{1}{x^2}$中，是整式的有____ 个．

B

    Scientists say life will be very different in 2050.

    First, there will be no TV channels (频道) in 2050. People will choose a program (节目) from a computer and watch it on TV. In 2050, we will get information from the computers only.

    Second, water will be a big problem in 2050. In many places, people won't have water to drink.

    Third, cars will use new and clean fuels (燃料) and they will go very fast. There will be a computer in every car. And the computers will control the cars and there won't be any accidents (事故).