阅读理解

    Turn left at the second crossing if you drive along Center Street north to south. If you come by bus, you can get off(下车) at the B. Street Bus Station. You can't miss it!

    Please come to the black door. Our party will be on the farm behind the house. Put your gifts into the small tent on the grass(草地). Remember : This is a surprise party, so do not let him know anything about it by the party.

    We will have a buffet lunch(自助餐) and later all kinds of interesting games for everybody!

    Music Show at 4 P.M.

    Bring your guitars, violins, drums and anything that makes sound！

    Please let me know by July 4^th if you can make it.

科学家观察组成物质的分子结构，需要借助（　　）

为了测量一古塔的高度，某人在塔的正西方向的A地测得塔尖的仰角为$45°$，沿着A向北偏东$30°$前进100米到达B地（假设A和B在海拔相同的地面上），在B地测得塔尖的仰角为$30°$，则塔高为（  ）