题干

在动物育种中,用一定剂量的X射线处理精巢,可得到大量的变异个体,这是因为(   )

A:合子都是纯合体

B:诱发了雄配子发生高频率的基因突变

C:诱导发生了大量的染色体变异

D:提高了基因的互换率

上一题 下一题 0.0难度 选择题 更新时间:2018-01-03 12:22:28

答案(点此获取答案解析)

B

同类题1

通读下面短文,掌握其大意,然后在各题所给的四个选项(A、B、C和D)中选出一个最佳选项。

     In New York City public schools, 176 different languages are1 among more than one million students.

     For 160,000 children, English is not their first language. New York's Department of Education 2 learning better for these students by providing dual-language programs. Students are usually taught3 two languages, English and 4, like Chinese or 5. Math, social studies, science and all other 6courses are taught in both languages. And they7the culture of the other country at the same time.

      Milady Baez is Deputy Chancellor of English Language Learners. She says these dual-language programs will help children 8 in the future. "The jobs of the future 9that our students know more than one language. They are going to be traveling 10. They are going to be communicating with people from all over the world. This will open doors for them."

      Shuya Zhang teaches a dual language class. She says the program helps children get ready 11work with people in other countries.   "Nowadays, America has started economic relationships with China. Lots of factories 12. They need people who 13 both practical skills and language skill."

     14these dual-language programs are popular, some groups in the U.S. think English should always comes first. "We have no problem with people speaking multiple (多种多样的) languages. It’s OK if people want to speak15different language at home. What we do think is schools should prioritize English."