人体的汗液中含有氯化钠，手触摸过物体后，指纹上的汗液就会留在物体上．因此法医做指纹鉴定的时候可选取的试剂是（ ）
A．酸碱指示剂
B．AgNO3溶液
C．酒精
D．碘酒
汗液中含有代谢产物氯化钠及一些油脂，A、C、D三种物质和氯化钠都不能反应产生现象，故没法提取指纹；用AgNO3溶液喷洒在留有指纹的物体上可发生反应 AgNO3+NaCl═AgCl↓+NaNO3
然后对物品进行热处理，氯化银受热分解，在物品上出现黑色斑迹，指纹就显现出来了．
故选B
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| I have a good mother. She has always made sure we eat very 1 . We live 2 the sea and have fish about four times a 3 . We eat fresh fruit and vegetables every day. We don't eat 4 sugar or fat (脂肪). A lot of my school friends eat many sweets every day but I only eat a few. And I'm not too heavy, so I 5 have to be thinner. I'm quite healthy. I don't often get cold, 6 I had a bad cold and a high temperature last week because I played football in the 7 I don't often get things 8 flu (流感) either. Last winter almost all my classmates got flu-but I didn't. I don't get these things 9 I take a lot of exercise and I am very 10 . Two years ago I broke my 11 while I was playing football and I couldn't 12 my arm for a month. So as you can 13 from what I've said, I'm an 14 person. But there's one thing I really love playing football. I'm captain of the class team at school. Because of this, I must have a good diet (饮食), and as I've said, this isn't a problem because my mother 15 us so well. | ||||
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