When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.

　　21. In the long run, the most difficult problem caused by population growth on earth will probably be the lack of______.

　　A. food B. oil

　　C. space D. resources

　　22. Carl Sagan believes that Venus might be colonized from earth because______.

　　A. it might be possible to change its atmosphere

　　B. its atmosphere is the same as the earths

　　C. there is a good supply of water on Venus

　　D. the days on Venus are long enough

　　23. On Venus there is a lot of______.

　　A. water B. carbon dioxide

　　C. carbon monoxide D. oxygen

　　24. Algae are plants that can______.

　　A. live in very hot temperatures B. live in very cold temperatures

　　C. manufacture oxygen D. all of the above

　　25. Man can eventually land on Venus only when______.

　　A. the algae have done their work B. the atmosphere becomes cooler

【人口的增长引发的社会危机以及应对的措施】相关文章：

★ 2013年最新的英语六级阅读练习题及答案3

★ 2009年6月英语六级阅读冲刺的倒计时倒数13天

★ 2012年12月暑期英语六级备考阅读每日一练 0808

★ 2013年12月英语六级外刊的阅读电池技术 一堆木头

★ 08年12月四级完形考前的练习第二十六篇的

★ 外刊阅读“书籍和互联网：你能看出它们的关联嘛？

★ 第1799期阅读理解附答案

★ 2011年最新六级阅读理解练习（46）

★ 英语四级阅读备考：真题长难句解析

★ 2011年最新六级阅读理解练习（27）