A.first markB.be first markedC.have first markedD.have ……

未分类题请阅读短文，完成第题。When we analyze the salt salinity（盐溶度 ） of ocean waters， we find that it varies only slightly from place to place. Nevertheless， some of these small changes are important. There are three basic processes that cause a change in oceanic salinity. One of these is the subtraction of water from the ocean by means of evaporation. In this manner， the salinity is increased， since the salt stays behind. If this is carried to the extreme， of course， white salt would be left behind; this， by the way， is how much of the table salt we use is actually obtained.The opposite of evaporation is precipitation， such as rain， by which water is added to the ocean. Here the ocean is being diluted so that the salinity is decreased. This may occur in areas ofhigh rainfall or in coastal regions where rivers flow into the ocean. Thus salinity may be increased by the subtraction of water by-evaporation， or decreased by the addition of fresh water by precipitation.Normally， in hot regions where the sun is very strong， the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation. Similarly， in coastal regions where rivers dilute the sea， salinity is somewhat lower than in other oceanic areas.

单项选择题根据《民法通则》规定，无效的民事行为。从()起就没有法律约束力。

单项选择题按生产工艺过程的作用原理分类，主要用于完成介质的流体压力平衡缓冲和气体净化分离的压力容器属于()容器。

单项选择题储气罐一般由()制造而成。

单项选择题对于某台压力容器，其以下压力值最大的是()