水是宝贵的自然资源，在工农业生产和日常生活中有着极其广泛的运用。如图为自来水厂净水过程示意图：

（1）图中吸附池内的活性炭起       作用，经沉淀、过滤等净化处理后所得的水        纯水(填“是”或“不是”)。

（2）家庭生活中可以用         检验某水样是硬水还是软水。

（3）有些科学家预言：“世界上最后一滴水就是人类的眼泪”。这句话警示我们应树立保护水资源的意识：一是节约用水，二是防止水体污染。请你举一例节约用水的做法：                 。

In (66) the strength of the carrier signal is varied to represent binary 1 or 0. (67) is a system that can map a name to an address and conversely an address to al name. (68) is a three-way handshaking authentication protocol that it’s packets are encapsulated in the point-to-point protocol. (69) is an approach that enables an ATM switch to behave like a LAN switch. (70) is an guided media which is made of glass or plastic and transmits signals in the form of light.

A．PPP

B．PAP

C．CHAP

D．LCP