题干

20年前,手机称“大哥大”,买一部要花2万多元,相当于当时一个普通工薪者20年的收入。最近,小薇只用300多元便买了一部,仅相当于一个普通工薪者一周的收入。手机价格降低的根本原因是

A:厂家数量增多使产品供应量增大

B:商家采用了薄利多销的销售策略

C:科技进步增加了商品的技术含量

D:劳动生产率提高使单位商品价值量减少

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答案(点此获取答案解析)

D

同类题4

            

             Parents who help their children with homework may actually be bringing down their school grades. Other forms of prenatal involvement, including volunteering at school and observing a child's class, also fail to help, according to the most recent study on the topic.
The findings challenge a key principle of modern parenting(养育子女) where schools except them to act as partners in their children's education. Previous generations concentrated on getting children to 
school on time, fed, dressed and ready to learn.
       Kaith Robinson, the author of the study, said, "I really don't know if the public is ready for this but there are some ways parents can be 
involved in their kids' education that leads to declines in their academic performance. One of the things that was consistently negative was
 parents' help with homework." Robinson suggested that may be because parents themselves struggle to understand the task." They may 
either not remember the material their kids are studying now, or in some cases never learnt it themselves, but they're still offering advice."
       Robinson assessed parental involvement performance and found one of the most damaging things a parent could do was to punish their children for poor marks. In general, about 20% of parental involvement was positive, about 45% negative and the rest statistically
 insignificant.
      Common sense suggests it was a good thing for parents to get involved because "children with good academic success do have involved
 parents ", admitted Robinson. But he argued that this did not prove parental involvement was the root cause of that success." A big 
surprise was that Asian-American parents whose kids are doing so well in school hardly involved. They took a more reasonable approach, conveying to their children how success at school could improve their lives."