中度以上龋，银汞合金充填时需垫底，是因为银汞合金有A．化学腐蚀性 B．流动成球性 C

读某地等高线地形图，回答下题：

小题1:图中①地和②地相差最有可能是：

A．100m

B．150m

C．200m

D．250m小题2:图中甲河的流向是：

A．从北向南

B．从西南向东北

C．从东北向西南

D．从南向北

阅读下文并回答问题。

Mr. King is from America. He and his wife are teachers. They teach English in a middle school in Beijing. They have two daughters. They are twins. Their names are Lucy and Lily. They're twelve. They look the same. They are students, but they are in different school. Their family has two bikes and a car. One bike is for Lily, the other is for Lucy. Mr. and Mrs. King go to work in their car. They have many friends in China. They sometimes go to the friends' home for supper（晚餐）.

小题1:Where is Mr. King from?

小题2: How do Mr. and Mrs. King go to work?

小题3: Do Mr. and Mrs. King have many friends in China?

油漆和防腐化合物防腐蚀的原理是通过涂层来阻断氧气的腐蚀。

制冷、空调系统安装结束后，除对制冷机及工艺系统进行检验和调试外，对自控系统也要进行检测、校验和调整。

我国规定气体的标准状态是指温度为（）压力为（）时的状态。