题干

 进行下列对比实验,不需要控制变量的是(  )

A:用酚酞溶液鉴别稀硫酸和氢氧化钠溶液

B:用红磷和白磷探究可燃物燃烧的条件

C:用MnO2、CuO和H2O2溶液比较MnO2、CuO的催化效果

D:用镁、锌和稀盐酸比较镁、锌的金属活动性强弱

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A

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    While it may seem like everyone surfs the web these days, there is fine line between casually checking your social media pages and having a full blown Internet addiction. If you fear that you may lose interest in other aspects of your life because you prefer to be on the Internet, you may be on your way to an Internet addiction. ____

Admit you are at risk of an addiction.

    More and more people in the world are becoming addicted to the Internet. You are not the only one with this problem; it is becoming more and more common and more and more well known. ____.

Set aside limited time for computer use.

    Make sure not to turn it on too many times a week. If you have a laptop, make sure to put it somewhere that you can remember but not somewhere that you see every day. Try keeping the lid closed when you are not using it; ____ If you have a desktop PC, try not to go near it or put something over it like a sheet.

Call people instead of sending instant messages or texts.

    If you are free on weekends, call friends and ask them to go outside. This will distract you from the computer. ____

Use an alarm clock or timer.

    Before using your computer, decide on a time limit such as 30 minutes. Set the clock or timer and make sure that you get off the computer when the time is up. Alternatively create a shutdown timer on your desktop. ____.

A. Make a small list of what you want to do within that time.

B. When the computer is not looking at you, you are less likely to use it.

C. This can be programmed to shutdown your computer after the set time

D. Luckily, there are ways to avoid living your life in front of the computer.

E. This will stop you from using the Internet so often or going on to another page.

F. If you have a problem on weekdays, phone your friends or ask for help in person.

G. Do not be embarrassed; find others with the same problem and help each other beat it.