单项选择题
1、根据以下资料，回答题。 　　Many people use wood stoves and fireplaces to heat their homes．Scientists have become worried about the smoke that they give off．Harmful chemicals are in the smoke．The smoke is causing air pollution．The pieces of pollution, called soot, are floating in the air．They are too tiny to see．Scientists must use a microscope to see them.
　　Small amounts of soot are safe, but large amounts can be dangerous．The govenment wants to limit this kind of pollution．It may stop people from using their fireplaces.
　　The air is tested every day．When soot levels are high, more than 65 micrograms of soot per cubic meter, factories must stop making smoke．The government thinks that limit should be much lower.
Factories produce the most smoke and soot．But the government thinks that all types of burning should be limited．The soot levels from factories and homes could be limited．Home owners may have to install new wood stoves that they comply with the new law．Or, they may not be able to bum on days when the air quality is bad.
　　Residents of some towns are fined if they violate the burning ban．Scientists hope these new regulations will make the air cleaner and less harmful to breathe.
Why is it dangerous to burn too much wood?
A． The fire could burn yo
B． It's not healthy to be too war
C． Harmful chemicals are released in the soo
D． The smoke is filled with unseeable tiny piece

2、刘某提前两周以600元订购了海鸥航空公司全价l000元的六折机票，后因临时改变行程，刘某于航班起飞前一小时前往售票处办理退票手续，海鸥航空公司规定起飞前两小时内退票按机票价格收取30%手续费。下列选项正确的是（　　）
A．退票手续费的规定是无效格式条款
B．刘某应当支付300元的退票手续费
C．刘某应当支付180元的退票手续费
D．航空公司只能收取退票的成本费而不能收取手续费

填空题
3、温室气体主要有          、          、          、         、         等。


简答题
4、



5、



6、已知二阶线性常系数齐次微分方程的两个特解，试写出相应的微分方程：


7、 简述种群分布的类型。


8、 Jack is good at playing__________ volleyball．


9、简述气质类型及其主要特征。

10、简述同时履行抗辩权的概念和适用条件。

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