问题补充：
March 20th is World Water Day every year. According to a report from the United Nations, more than half of the worlds major rivers have serious water loss and are polluted.
The Yellow River, the worlds fifth longest river, watered some of the oldest farms on earth. But now it has a serious problem. 【小题1】In most of the past 35 years, it didn reach the sea.
The Nile in Egypt, running 6, 650 km, is the longest river in the world. 【小题2】Now it is down to 2 billion m or so. Australias Murray River reaches the sea only every other year. One fifth of Americas Rio Grande has no water, either.
【小题3】
Mostly its damming (筑坝) and global warming that make rivers dry.
【小题4】Now about 45, 000 of them lie across the worlds rivers. They hold back around 15% of the worlds fresh water from running to the sea.
Global warming is making things worse. Warmer weather takes water away. The glacier (冰川) are becoming smaller. 【小题5】Global warming has had certain effects on water sources (源头). Droughts (干旱) happening around the world make people pay more attention to this fact.
A．Dams hold water to irrigate (灌溉) fields and make power. B．The source of the Yellow River is drying up because of it.C．It used to carry 32 billion m of water a year.D．How does it happen?E. Factories pour waste water into rivers directly.
F. Its source on Qinghai-Tibet Plateau is drying up.
F
答案：
(答案→)F
解析：从方框中所给的选项中选出能填入空白处的最佳选项，补全短文，其中有一项为多余选项。（10分）
文章大意：每年的3月20日是世界水日。根据美国的一个报道，世界上有一半多的主要河流严重缺水或被污染。黄河，世界上第五大河，在过去的35年里，就没有流到大海里。同意，埃及的尼罗河，世界上最长的河流，由原来每年的32000000000平方米的流量降低到2000000000.等等。是说明原因造成这样的现象？主要是由于筑坝和全球变暖导致河流干涸。
