题干

物理研究中常常用到“控制变量法”、“等效替代法”、“转换法”、“类比法”等方法,在下面初中物理的几个研究实例中,采用了“等效替代法”的是(   )

A:研究电流时把它与水流相比

B:用总电阻来替换各部分电阻在电路中的共同作用

C:通过煤油温度的变化来显示电流做功的多少

D:研究电流大小与电压的关系时,保持电阻一定

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B

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Drug problems

    If you're worried about your own or someone else's drug taking or misuse, it's good to know the facts.

Why take drugs?

    Drug users don't start using drugs with the intention of becoming addicted. But many drugs contain addictive substances(物质) and even people who use them occasionally can become dependent and need to use them regularly.

    Reasons why people start using drugs can include: to escape problems they may be having in other parts of their life, peer pressure and fitting in with another group of people, being curious about the effects of drugs.

    If you start to use drugs on a regular basis, or if you become dependent on them, it can affect your family and friends as well as having a serious impact on your own physical and mental well-being.

    Drug overdoses can be fatal. You can die instantly from misusing substances and drugs that you can buy over the counters.

Signs of drug abuse and misuse

    There is not a common list of symptoms that you can use to tell if you or someone you know is misusing drugs. That's because drug use affects different people in different ways, depending on the type of drugs they're using.

    Although anxiety, tiredness and a change in sleeping habits can be signs of drug use, they can also be caused by changes in your body, stress or other problems.

_____________________

    Drugs are categorised into three classes based on their overall level of harm. Class A drugs are the most dangerous, however, all the drugs in all three classes are harmful and addictive.

    Remember that all drugs are illegal, even Class C drugs like cannabis(大麻烟). If you're caught selling them to other people, or carrying a small amount in your pocket, it's likely that the police will get involved.

    If you're found guilty of any of these offences, you may face a fine or time in custody(拘留), with Class A drugs carrying the most severe sentences.

Worried about a friend?

    If you think that one of your friends or relatives is misusing drugs, you may want to approach them and talk about it. It's not your responsibility to make them stop, but you can tell them about how their behaviour is affecting your relationship.

    If they ask for help with their problem, then it's important to listen and help them find the right information and treatment.

National Drugs Helpline

    If you're worried about drug abuse and addiction you can call the National Drugs Helpline on 0800 776 600 for confidential advice—lines are open seven days a week. Calls are free and they won't show up on your phone bill, but you may be charged if you use a mobile.

More useful links

Information about addictions from need to know

Information about drugs, the law and human rights