-Why does the Lake smell terrible? 

-Because large quantities of water       .  

A．have polluted

B．is being polluted

C．has been polluted

D．have been polluted

下列叙述正确的是                                          

A．常温下pH=12的烧碱和pH=2的盐酸溶液等体积混合，混合液的pH =7

B．pH相同氨水和烧碱溶液稀释相同倍数时，它们的pH仍相同

C．同浓度盐酸中和pH相同的氨水和烧碱溶液，

D．向一定量纯水中通入少量HCl气体后，Kw值增大