题目

Typhoons(台风)are some of the worst storms,ususlly around the Pacific Ocean and South China sea.Most happen in July,August and September. How does a typhoon happen?When lots of seawater gets hot in the summer sun,it evaporates into the air.This makes the air hotter.When the air gets warm enough,it starts to move higher up into the sky.Then,cooler air around it rushes in .It fills the space that is left.After the air gets warmer ,it starts to move quickly,making wind.The wind goes in circles,and it keeps moving hgher in the sky.The warmer the air gets,the quicker the wind moves.And wh制作潜望镜时，需要用到的两个镜子是 [　　] A．平面镜B．一个凸透镜，一个平面镜 C．凹透镜D．一个凸透镜，一个凹透镜