题目内容
（请给出正确答案）
What type (or types)of intermolecular attractive forces are found in the following？
(1)HCl (2)NO (3)Ar (4)CO2
(5)CCl4(6)H2S (7)HF (8)SO2
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Over vast areas of every continent,the rainfall and vegetation necessary for life are disappearing.Already more than 40 percent of the earth's land is desert or desertlike.About 628 million people—one out of seven—live in these dry regions.In the past,they have managed to survive,but with difficulty.[ZZ(Z]Now largely through problems caused by modern life,their existence is threatened by the slow,steady spread of the earth's deserts. Scientists still do not understand all the complex problems of the desert,but there have been many ideas for saving the land.Sandi Arabia has planted 10 million trees to help keep the sand from taking over fertile areas.The Israelis are aga in using some of the water collection systems left by the ancient people in the Negev desert.They plan to water their orchards with the extra water.Some Sahel farmers still raise cattle on their poor farm land,but before the cattle are sold, they are taken to greener lands in the south to get fat.
26. What is the article mainly concerned？
A.The problem of spreading desert.
B.The rainfall and vegetation in desert areas.
C.The water collection systems.
D.The difference between modern life and ancient life.
27. “one out of seven” refers to____.
A.more than a third of the lands' earth
B.the percentage of the earth's land that is desert-like
C.the number of people who live in dry regions
D.a day of a week
28. In paragraph 2,“they are taken to the greener lands in the south.”They refers to____.
A.the Sahel farm land
B.the farmers
C.the cattles
D.the trees
29. How many ideas for saving the land are described？
A.Five. B.Two. C.Four. D.Three.
30. Which of the following statements is true, according to the passage？
A.The earth's desert are slowly spreading.
B.One out of 10 people lives in dry regions.
C.Their life in the desert is threatened now by traditional problems.
D.New water wells can solve the problem in Africa's desert.
H2O的沸点是100℃，H2Se的沸点是-42℃，这可用下列哪种理论来解释( )。
(A) 范德华力 (B) 共价键 (C) 离子键 (D) 氢键
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