题干

如图甲所示,是某型号电压力锅简化的工作电路图.R0是阻值为484Ω的保温电阻,R1是规格为“220V 800W”的主加热电阻,R2是副加热电阻.电压力锅煮饭分为“加热升压→保压→保温”三个阶段,通过如图乙所示的锅内工作压强与时间“(P﹣t)”关系图象可了解其工作过程:接通电源,启动智能控制开关S,S自动接到a,同时S1自动闭合,电压力锅进入加热升压状态;当锅内工作压强达80kPa时,S1自动断开,进入保压状态,当锅内工作压强降至60kPa时,S1又会自动闭合;当保压状态结束,饭就熟了,S自动接到b,减压进入保温状态.电压力锅煮饭时,在正常加热升压和保压状态共耗电0.25kW•h,下列正确的是(   )

A:电压力锅是对大气压强的应用

B:当锅内工作压强为40kPa时,电压力锅处于升压状态

C:电压力锅煮饭时,在正常加热升压和保压状态R1的工作时间是18min

D:R2正常工作时的电功率为300W

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D

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    Nowadays, parents worry a lot because their children spend hours and hours in front of the TV screen. Because this doesn't happen to only one specific family, many experts warn us that there can be some serious effects of children watching violence on television.

    Children who become addicted(上瘾的) to TV sit down and turn on the TV as soon as they get home. Although they have lots of homework, they become absorbed in TV programs.

    Since they spend tons of time watching TV, they have less time to enjoy real life activities such as playing with friends, playing outdoor sports, or enjoying other kinds of entertainment.

    There are too many violent scenes on TV. Some experts say there are 25 acts of violence per hour on TV. In addition, there are many experiments by psychologists which show how TV violence influences children. Finally, people worry that children tend to imitate what they watch on TV and may start to behave more violently.

    What should be done? First of all, the government should regulate TV violence. It should also encourage people to invent and develop new technology which can block violent scenes from the programs children watch. For example, with a rating system(分级制度) and the V-chip, unfit scenes of violence and sex can be blocked out. Second, parents should monitor what their children watch. At the same time, they should make their children interested in real life activities. Then when the children start to spend more time playing with friends or reading books, parents can stop their monitoring.

    It is a fact that there is more violence on TV today than there was ten years ago. Moreover, violent incidents occur more frequently in real life. It's time to realize how harmful watching TV violence is, and it's time to keep our children from watching violence.