问题 选择题

生男生女的机会均等,其原因是(  )

A.含X染色体和含Y染色体的两种精子与卵细胞结合的机会均等

B.含X染色体和含Y染色体的两种卵细胞与精子结合的机会均等

C.精子有一种类型,而卵细胞存在两种类型

D.雄性激素和雌性激素的作用机会均等

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.女性则只产生一种含X染色体的卵细胞,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.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.这说明男女的性别在受精卵形成时就已确定.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.

故选:A.

阅读理解

Michael Jackson is one of the world’s best singers. Michael Jackson was born in the middle west of the city of Gary, Indiana, in 1958. He began singing with his four brothers. They called the group “The Jackson Five”. The group became very popular after appearing on a television program. They started singing in 1965, and became popular soon. In 1970 the group made their first record with the name of “I Want You Back”. It was very popular. One of their hit records was “Never Say Goodbye”.

Michael was good at dancing as well as singing, for example, his dance moves and moon walking. He was asked to act in a film in 1978 for the first time, and in the same year he made a record on his own, which sold eight million copies all over the world.

Michael nearly didn’t go out because he was too famous. Once his fans went off in a faint(晕倒) when they saw him at the concert. No one can do it by now. He lived in a large house and kept lots of animals. He never ate meat. He often raised money for Charity. This made him win the Guinness World Records(吉尼斯世界记录)in 2006. He died on June 25th, 2009, but he would live in our heart forever.

小题1: How many people are there in Michael’s group?

A.Three.

B.Five.

C.Four.

D.Six.小题2: What’s the name of their first record?

A.“Never Say Goodbye”.

B.“See You, See Me”.

C.“I Want You Back”.

D.“On the World”.小题3: The underlined word “copies” means          in Chinese.

A.抄写

B.张/份

C.复制

D.模仿小题4: Michael was good at         according to the passage.

A.rock music

B.street dance

C.playing the piano

D.moon walking小题5:Why did Michael have to stay at home most of time?

A.Because he was too famous.

B.Because he often felt lonely.

C.Because he had no friends.

D.Because his company asked him to do so.

单项选择题