搜题请搜索小程序“爱下问搜题”
问题 选择题

下列关于基因说法正确的是（　　）

A．基因是染色体上的一个片段

B．基因是DNA分子上任意一片段

C．基因是染色体的另一种说法

D．基因是具有特定遗传效应的DNA片段

答案

染色体是细胞核中容易被碱性染料染成深色的物质，染色体是由DNA和蛋白质两种物质组成；DNA是遗传信息的载体，主要存在于细胞核中，DNA分子为双螺旋结构，像螺旋形的梯子；DNA上决定生物性状的小单位，叫基因．基因决定生物的性状．基因位于染色体上，基因是DNA分子上的一个个小片段，这些片段具有特定的遗传信息，能够决定生物的某一性状，一个基因只具有特定的遗传信息．

故选：A

单项选择题

二类精神药品为（）

A．阿司匹林

B．亚砷酸钾

C．布桂嗪（强痛定）

D．眠尔通

E．芬太尼
查看答案
单项选择题

Modern industrial society grants little status to old people. In fact, such a society has a system of built-in obsolescence. There is no formal system for continuing our education throughout our life in order to keep up with rapidly changing knowledge. When our education and job skills have grown obsolete, we are treated exactly like those who have never gained an education or job skills and are not encouraged or given the opportunity to begin anew.As a society becomes more highly developed, the overall status of older people diminishes. Improved health technology creates a large pool of old people, who compete for jobs with the young. However, economic technology lowers the demand for workers and creates new jobs for which the skills of the aged are obsolete, forcing older people into retirement. At the same time, young people are being educated in the new technology and are keeping pace with rapid changes in knowledge. Finally, urbanization creates age-segregated neighborhoods. Because the old live on fixed incomes, they must often live in inferior housing. All these factors — retirement, obsolete knowledge and skills, inferior standards of living — lower the status of the aged in society.A century ago, when one could expect to live only to 50 or so, the life span more or less coincided with the occupation and family cycle. But today the average life span allows for fifteen to twenty years of life after these cycles. It appears that our life span is outpacing our usefulness in society.

Which of the following would be the best title for this passage

A．The Problem of Aging

B．Social Structures

C．Economic Technology

D．Continuing Education
查看答案