确定基准收益率的基础是( )，而投资风险和通货膨胀是必须考虑的影响因素。A．生产成

阅读理解

     About 21,000 young people in 17 American states do not attend classes in school buildings.Instead,

they receive their elementary (初等) and high school education by working at home on computers.The

Center for Education Reform says the United States has 67 public "cyberschools", and that is about twice as many as two years ago.

     The money for students to attend a cyberschool comes from the governments of the states where they

live.Some educators say cyberschools receive money that should support traditional public schools.They

also say it is difficult to know if students are learning well.

     Other educators praise this new form of education for letting students work at their own speed.These

people say cyberschools help students who were unhappy or unsuccessful in traditional schools.They say

learning at home by computer ends long bus rides for children who live far from school.

     Whatever the judgment of cyberschools, they are getting more and more popular.For example, a new

cyberschool called Commonwealth Connections Academy will take in students this fall.It will serve

children in the state of Pennsylvania from ages five through thirteen.

     Children get free equipment for their online education.This includes a computer, a printer, books and

technical services.Parents and students talk with teachers by telephone or by sending emails through their

computers when necessary.

     Students at cyberschools usually do not know one another.But 56 such students who finished studies at Western Pennsylvania Cyber Charter School recently met for the first time.They were guests of honor at

their graduation.

1. What do we know from the text about students of a cyberschool?

A. They have to take long bus rides to school.

B. They study at home rather than in classrooms.

C. They receive money from traditional public schools.

D. They do well in traditional school programs.

2. What is a problem with cyberschools?

A. Their equipment costs a lot of money.

B. They get little support from the state government.

C. It is hard to know students' progress in learning.

D. The students find it hard to make friends.

3. Cyberschools are getting popular because ________.

A. they are less expensive for students

B. their students can work at their own speed

C. their graduates are more successful in society

D. they serve students in a wider age range

4. We can infer that the author of the text is ________.

A. unprejudiced in his description of cyberschools

B. excited about the future of cyberschools

C. doubtful about the quality of cyberschools

D. disappointed at the development of cyberschools

煤粉尘有哪些危害？

精细化工技术中（）是关键。

果蝇红眼对白眼为显性，控制眼色的基因位于X染色体上，双亲中一方为红眼，另一方为白眼，杂交后代中雌果蝇与亲代中的雄果蝇眼色相同，雄果蝇与亲代的雌果蝇相同。下面叙述不正确的是（）

A.亲代雌果蝇和雄果蝇的体细胞中都不存在等位基因

B.F1雌雄个体交配，F2中出现红眼果蝇的概率为3／4

C.F1雌雄个体交配，F2中各种表现型出现的概率相等

D.F2雌雄个体基因型不是与亲代相同，就是与F1相同

声波有多种表示方法，常用的有数学公式、（）或者（）等。