下列有关细胞生命历程的说法，错误的是（）。
A.细胞分化过程中，mRNA的种类发生变化，使生物体中的细胞趋向专门化
B.体细胞癌变后，生理状态发生改变，细胞核全能性丧失
C.细胞衰老过程中，代谢减弱；细胞癌变过程中，代谢增强
D.被病原体感染的细胞的清除.是通过细胞凋亡完成的
参考答案：B
解析：细胞分化过程中，由于基因的选择性表达，转录成的mRNA种类不同，使生物体中细胞的功能趋向专门化，A正确；细胞癌变后，生理结构和形态发生了改变，成为不死细胞，但细胞核具有的全部遗传信息都在，全能性没有丧失，B错误；衰老细胞的代谢逐渐减弱，癌变的细胞不断增殖，代谢旺盛，C正确：效应T细胞攻击靶细胞，导致被病原体感染的细胞自动裂解死亡就是细胞凋亡过程，D 正确。
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| Quality after-school programs are designed to improve academic performance, decrease youth crimes and other high-risk behaviors, and help young people grow into healthy, successful adults. The effect of quality after-school programs on academic performance is clear. Studies show that students who take part in such programs show better work habits, higher rates of homework completion, improved grades, and higher scores on achievement tests. They also have fewer absences and are less likely to blame. After-school programs also influence high-risk teen behaviors. Various studies show decreased rates of crime, drug-taking, and teen sex among youth who join in well-run after-school programs when compared to similar youth who do not. Finally, after-school programs play an important role in supporting different kinds of fields of development: physical development, mental development and social development. Thus, one can safely say that after-school programming is an effective method to help young people become contributing members of society. Although there is enough proof from both small and large assessments that after-school programs can make a positive difference, it is important to note that not all programs are equal. First, dosage matters-young people who attend the most hours over the most years benefit more than members who attend less often or over a shorter period of time. Next, after-school programs make a bigger difference for those students who need help most and have the fewest choices. Finally, program qualities matter. After-school programs work best when they create unique opportunities for youth. They should provide opportunities, skill building meaningful involvement, expression, suggestion, service, and work. Staff characteristics make an important difference in the quality of a program. The adults should treat youth as partners, create safe and fair environment, encourage personalized involvement, and actively create learning opportunities. In short, although after-school programs have a promising future, how they are designed and run matters. | ||||||||||
Title: Quality After-school Programs
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