My name is Lily. I'm from London. This is my mother. She is an English teacher. She is good at cooking and she is nice. This is my father. He is thin(瘦的)and short. He is clever. I love them. Oh, this is my house. Is it beautiful? The famous Thames(泰晤士河) is close to my house. It is long. There are a lot of ships on the river(河). I like watching the ships.

到滑雪场滑雪是十分受人喜爱的项目，一般滑雪场都是人工造雪，人工造雪的关键是获得超低温，获得超低温的方法是：来自高压水泵的高压水与来自空气压缩机的高压空气在双进口喷嘴处混合，如图所示，水泵将水从喷口处大范围扬起，利用水____降低水的温度；空气压缩机高压空气从喷嘴喷出后，体积膨胀，通过____的方式使气体的内能减小，温度降低，两个方面的作用形成的低温使喷口扬起的水滴____变成冰雪．

$\tan {300}^{°}$=（    ）

我国在新农村建设中，为了改善农村卫生条件，改变能源结构，减少环境污染，大力推广兴建沼气池．在沼气发酵中，起主要作用的微生物是（　　）

下列说法正确的是