题目

完形填空 Many people argue that working can be a valuable experience for the young. However, working more than about 15 hours a week is 1 for teens because it reduces their involvement with school, and 2 a materialistic and expensive lifestyle. Schoolwork and the benefits of extracurricular activities tend to be 3 when teens work long hours. As more and more teens have filled the many part-time jobs, teachers have faced increasing 4. They must both keep the attention of 5 pupils and give homework to students who simply don't have time to do it.6, educators have noticed less involvement in 人体在正常情况下，下列生理过程能够发生的是A．相同的RNA逆转录合成不同的DNA        B．相同的DNA转录合成不同的RNAB．相同的密码子决定不同的氨基酸         D．相同的tRNA携带不同的氨基酸