【科学60秒】犯罪现场调查：血迹测龄_英语听力练习mp3下载-科学-沪江听力酷

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【科学60秒】犯罪现场调查：血迹测龄

听力简介：

You’ve seen it on TV. Crime scene investigators ____1____ what might be a murder scene. There are blood ____2____ — but no body. Who’s the victim? Now, a new technique developed in the Netherlands might help real-world investigators establish the age of the victim using only blood. The research was published in the journal Current Biology.
Usually, age is determined by physical characteristics, such as teeth or bones. Great—if you have a body. Researchers have tried unsuccessfully to use blood. But in this study, the scientists used immune cells called T-cells. T-cells ____3____ receptors that match molecules on bacteria, viruses, even tumors. The cellular activity that produces these receptors also produces a type of circular DNA molecule as a by-product.
The number of these receptor by-products declines regularly over time. So scientists devised a test to measure the molecules — and use that to infer someone’s age based on his or her blood. The results appear to ____4____ nine years. So forensic scientists could use a bloodstain to ____5____ a victim’s age to ____6____ two decades. That’s a big range—but it could help solve crimes when the victims can’t be found.
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