具有支持和保护作用的结构是（  ）

根据短文内容，选择最佳答案。

Scientists say life will be very different in 2050.First,there will be no TV channels (频道) . People will choose a programme (节目) from a computer and watch it on the television. We will get information on the computers only.

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

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