题干

如图所示,圆环a和圆环b的半径之比为2∶1,两环用同样粗细、同种材料制成的导线连成闭合回路,连接两环的导线电阻不计,匀强磁场的磁感应强度变化率恒定.则在a、b环分别单独置于磁场中的两种情况下,M、N两点的电势差之比为(       )

A:4∶1

B:1∶4

C:2∶1

D:1∶2

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答案(点此获取答案解析)

C

同类题4

根据短文内容,从下列A-F选项中选出能概括每一段主题的最佳选项。 选项中有一项为多余项。

A. Wash yourself as often as possible

B. Avoid being in hot sun

C. Keep away from smoke and alcohol

D. The importance of skin

E. Have a balanced diet

F. Be sure to have enough water

    ____When it comes to your skin, there is an important fact that you must keep in mind: Your skin is the largest organ of your body. Therefore, skin health and protection is crucial. Your skin does everything for you. It can keep your body hydrated and regulate your body's temperature.

    Now, here are some helpful tips for you to protect your skin:

    ____Protection against harmful rays from the sun is one of the most important steps that you need to take. With this in mind it is necessary for you to avoid strong sunlight as often as possible. As for sunscreen you need to buy products that contain UVA-1, UVA-2 and UVB protection.

    ____Your diet also has a direct impact on the health of your skin. The most important aspect of your diet in relation to the health of your skin is to make certain that you eat a proper amount of food items that contain the proteins and nutrients necessary for cellular maintenance, repair and regeneration.

    ____Water is also important to the health of your skin. While you certainly have heard it before, it actually is true that you should drink at least eight 8-ounce glasses of fresh water every day. There are many health benefits to be derived from drinking water daily, including maintaining healthy skin.

    ____Finally, when it comes to the health of your skin today and into the future you should avoid smoking all together. In addition, you should drink alcohol only in moderation. Both smoking and excessive alcohol consumption can negatively impact the health of your skin in significant ways.