题干

无土栽培技术是一种新型农业技术,已经广泛应用于粮食、蔬菜和花卉的生产。使用营养液栽培植物时,需要不断向营养液中通入空气(如图),这样做最主要的目的是(    )

A:促进蒸腾作用进行

B:促进根的呼吸作用

C:促进无机盐的吸收

D:促进叶的光合作用

上一题 下一题 0.0难度 选择题 更新时间:2016-06-03 11:09:32

答案(点此获取答案解析)

B

同类题5

阅读下面的短文,从短文后各题所给的四个选项(A、B、C和D)中,选出最佳选项。

How Women Were Freed From Their Homes

    As late as 1800, a woman's only place was in her home. Women in business were unheard of. No respectable woman would dream of entering what was strictly a “man's world”. Even if she would, what could she do? Men were sure that no woman could do a job well outside her home.  This was a widely-accepted idea. When the famous Bronte sisters began writing books in 1846, they had to resort to using men's names as aliases.

    Teaching was the first profession opened to women, soon after 1800. But even that was not easy for women to take because most high schools and colleges were open only to men. Oberlin College in Ohio was the first college in America to take in women.

    Nursing was regarded as a respectable profession for women only after Florence Nightingale won high credit for her nursing career and became famous. Miss Nightingale opened the first training school for nursing in 1860 in England.

    The invention of typewriters in 1867 helped to bring women out of their homes to join the business world. Because women are careful and have nimble fingers, businessmen found that they were well suited to this kind of work.

    By 1890, tens of thousands of women were working in schools, hospitals, shops, offices, and factories both in England and the States. Some even managed to become doctors or lawyers. The idea of women working in business and other circles was accepted.