问题 选择题

一个有耳垂(Aa)的男性和一个无耳垂(aa)的女性结婚,生下有耳垂子女的概率是(  )

A.100%

B.75%

C.50%

D.25%

答案

在生殖过程中,有耳垂的男性产生两种类型的精子:含A基因的精子和含a基因的精子,无耳垂的女性只产生一种类型的卵细胞,是含a基因的卵细胞;形成受精卵时,两种类型的精子与含a基因的卵细胞结合的几率是相等的,因此一个有耳垂(Aa)的男性和一个无耳垂(aa)的女性结婚,生下有耳垂子女的概率是50%.如图所示:

故选:C

单项选择题
阅读理解

The story of English language is a story of change.The old English language, or old English, is quite different from Modern English.If we do not study old English, we can’t understand it.Some of the words are the same, but many are not used now.The story of the English language begins some time after the year 400 AD.At this time, some people came to England from North-west Europe.There were many groups of people.They were called Angles (盎格鲁人), Saxons(撒克逊人)and Jutes(朱特人),whose language, old English, is like some of the modern language of North-West Europe.In old English, the ending had many meanings.They showed past time and present time and many other things.In Modern English, most of these endings are gone.This is the biggest difference between Old and Modern English.

小题1:What does the first sentence of the passage mean?

A.The story of English language often changes.

B.English is a language that has changed a lot as time passes by.

C.The old English language has changed into Modern English.

D.The story of English language is one of how people change the language.小题2:Old English has a story of ______.

A.2,500 years

B.more than 1,600 years

C.2,300 years

D.more than 400 years小题3:Old English was first used by the people from ______.

A.Old English

B.English

C.North-West English

D.North-West Europe小题4:Which of the following is NOT true about Old English?

A.The endings of words gave different special meanings.

B.It is easy for most English-speakers today to understand the language.

C.Its words are very different from those Modern English.

D.It was spoken by many groups of the people from North-West Europe.