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 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 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）.

下列物质在氧气中燃烧的现象，正确的是（     ）

2016年9月15日，“天宫二号”在中秋之夜完美升空，中国航天自信迈向空间站时代。请按要求完成下面各项任务。

如图所示，一个挂在绝缘细线下端的带正电的小球B，静止在图示位置，若固定的带正电的小球A的电荷量为Q，B球的质量为m，带电荷量为q，θ=30°，A和B在同一条水平线上，整个装置处于真空中．求：