Will there always be 31       water? When you consider how necessary water is to each and every one of us and to all 32     (live) things, and when you observe how man has mismanaged other 33     (nature) resources, you may have reason to worry. Man has badly polluted his sources of water 34    Earth. And he uses more and more water each day. Can man learn to treat 35      (pollute) water for reuse fast enough 36      (keep) pace with the world’s technology and   37    (grow) population?

At the present time there is no serious shortage of water in the United States. Water, however, is not 38     able to meet all the local needs. Some areas, such as the southwestern part of our country, get less rain than 39    . In these areas, water must be brought in from 40      outside. Los Angeles, for example, must obtain its water from sources hundreds of miles away in the Colorado River and the rivers of northern California.

下列哪项是由于经旁路传导异常所致的心律失常（）

A.逸搏及逸搏性心律

B.窦性心动过缓

C.心房颤动

D.室性早搏

E.预激症候群