问题 选择题

一对夫妇生育第一胎是女孩,生育第二胎是男孩的可能性多大(  )

A.25%

B.50%

C.100%

D.10%

答案

在亲代的生殖细胞形成过程中,经过减数分裂,两条性染色体彼此分离,男性产生两种类型的精子--含X染色体的精子和含Y染色体的精子.女性则只产一种含X染色体的卵细胞.受精时,如果是含X的精子与卵子结合,就产生具有XX的受精卵并发育成女性;如果是含Y的精子与卵子结合,就产生具有XY的受精卵并发育成为男性.由于男性可产生数量相等的X精子与Y精子,加之它们与卵子结合的机会相等,所以每次生男生女的概率是相等的.在整个人群中男女性别之比大致1:1.人的性别遗传如图:

从图中也可以看出每次生男生女的概率是相等的.因此一对夫妇第一胎生了一个女孩,那么第二胎生男孩的几率是50%.

故选B.

填空题
阅读理解

For the most part, you are probably only exposed to the music that is played on your favorite radio stations and TV shows, music Web sites, or the music that your friends and family members enjoy. While you probably know a lot about your favorite type of music, it can be a rewarding experience to enlarge your horizons(眼界), discovering artists and types of music that you’re not familiar with. Who knows, you might discover you like certain types of music you never even considered.

Have you ever wondered about the history and influences of your favorite types of music ? For example, did you know that rock ‘n’ roll originated(起源)from the blues, and that the blues began as a form of musical expression for African Americans during slavery(奴隶制度)?Did you know that most hip-hop is heavily influenced by early rhythm blues and jazz ?

There are many fun ways to learn about different musical styles and their historical roots. For example, if you like hip-hop, listen to some of your favorite CDs and take note of the samples the performers used to create the songs. There is a possibility that the artist used parts of older songs to create the music. You can go to the library or online to learn more about the artists and listen to more of their music by checking out CDs from the library or downloading songs online for a small fee.

You can learn so much about culture and history just by paying attention to different types of music and what is being expressed in the songs. There are so many different styles of music to learn about, and you owe(欠)it to yourself to make an effort to listen to and learn about them.

小题1:The main topic of this passage is _____.

A.creating music

B.performing music

C.enjoying your favorite music

D.learning about music小题2:What music did African Americans use to express their feelings of being slaves ?

A.Rock ‘n’ roll.

B.The blues.

C.Hip-hop.

D.Jazz.小题3:How can you learn about culture and history through music ?

A.By writing down the names of the music.

B.By creating music from older songs yourself.

C.By caring about what is being expressed in music.

D.By keeping a record of fees after downloading songs online.小题4:By saying the underlined sentence in the last paragraph, the author probably means that _____.

A.you should try harder to learn about music

B.you should return something to music

C.you should borrow music CDs from others

D.you should buy music CDs yourself