如图为演示自感现象的电路图，对于电路可能发生的情况，正确的说法是( )
A．当开关由断开闭合时，灯泡不会立即发光
B．当开关由断开闭合时，灯泡会立即发光，但会逐渐变暗直到稳定
C．当开关由闭合断开时，灯泡不会立即熄灭
D．当开关由闭合断开时，灯泡不可能比开关闭合时更亮
BC
本题考查自感现象。开关由断开闭合时由于线圈的自感作用刚开始线圈电流很小且逐渐变大，灯泡立即发光，通过线圈的电流逐渐变大，灯泡两端的电压逐渐减小，亮度逐渐减弱，线圈中电流稳定后灯泡亮度稳定，A错误B正确；开关由闭合断开时，由于线圈的自感作用，灯泡不会立即熄灭，可能闪亮一下再熄灭，C正确D错误；选BC。
根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。 Smiling is a great way to make yourself stand out while helping your body to function better. Smile to improve your health, your stress level, and your attractiveness; 1 We are drawn to people who smile．There is an attraction factor．We want to know a smiling person and figure out what is so good because anxieties can push people away, but a smile draws them in． Smiling changes our mood． Next time you are feeling down, try putting on a smile． 2 Smiling can trick the body into helping you change your mood． Smiling is appealing． When someone is smiling they lighten up the room, change the moods of others, and make things happier．A smiling person brings happiness with them．Smile a lot and you will draw people to you． Smiling relieves stress． Stress can really show up in our faces．Smiling helps to prevent us from looking tired, worn down, and overwhelmed． 3 The stress should be reduced and you’ll be better able to take action． Smiling lowers your blood pressure． When you smile, there is a measurable reduction in your blood pressure．Give it a try if you have a blood pressure monitor at home．Sit for a few minutes and take a reading．Then smile for a minute and take another reading while still smiling．____4____ Smiling lifts the face and makes you look younger． The muscles we use to smile lift the face, making a person appear younger．Don’t go for a face lift, just try smiling your way through the day—you’ll look younger and feel better． 5 Try this test: Smile．Now try to think of something negative without losing the smile．It’s hard．When we smile, our body is sending the rest of us a message that "Life is Good! "
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