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This is Scientific American's 60-Second Science. I'm Cynthia Graber. This will just take a minute.
You've seen it on TV. Crime scene investigators¹ show up at what might be a murder scene. There are blood spatters—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 determined² 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 recognize invaders³ through receptors that match molecules⁵ on bacteria, viruses, even tumors. The cellular⁶ activity that produces these receptors also produces a type of circular DNA⁷ molecule⁴ as a by-product⁸.
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 be accurate to within plus or minus nine years. So forensic⁹ scientists could use a bloodstain to narrow a victim's age to within two decades. That's a big range—but it could help solve crimes when the victims can't be found.
Thanks for the minute. For Scientific American's 60-Second Science, I'm Cynthia Graber.

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1 investigators
n.调查者，审查者( investigator的名词复数 )
参考例句：
This memo could be the smoking gun that investigators have been looking for. 这份备忘录可能是调查人员一直在寻找的证据。 The team consisted of six investigators and two secretaries. 这个团队由六个调查人员和两个秘书组成。来自《简明英汉词典》

2 determined
adj.坚定的；有决心的
参考例句：
I have determined on going to Tibet after graduation.我已决定毕业后去西藏。 He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。

3 invaders
入侵者，侵略者，侵入物( invader的名词复数 )
参考例句：
They prepared to repel the invaders. 他们准备赶走侵略军。 The family has traced its ancestry to the Norman invaders. 这个家族将自己的世系追溯到诺曼征服者。

4 molecule
n.分子，克分子
参考例句：
A molecule of water is made up of two atoms of hygrogen and one atom of oxygen.一个水分子是由P妈̬f婘̬ 妈̬成的。 This gives us the structural formula of the molecule.这种方式给出了分子的结构式。

5 molecules
分子( molecule的名词复数 )
参考例句：
The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。 Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

6 cellular
adj.移动的；细胞的，由细胞组成的
参考例句：
She has a cellular telephone in her car.她的汽车里有一部无线通讯电话机。 Many people use cellular materials as sensitive elements in hygrometers.很多人用蜂窝状的材料作为测量温度的传感元件。

7 DNA
(缩)deoxyribonucleic acid 脱氧核糖核酸
参考例句：
DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。 Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

8 by-product
n.副产品，附带产生的结果
参考例句：
Freedom is the by-product of economic surplus.自由是经济盈余的副产品。 The raw material for the tyre is a by-product of petrol refining.制造轮胎的原材料是提炼汽油时产生的一种副产品。

9 forensic
adj.法庭的，雄辩的
参考例句：
The report included his interpretation of the forensic evidence.该报告包括他对法庭证据的诠释。 The judge concluded the proceeding on 10:30 Am after one hour of forensic debate.经过近一个小时的法庭辩论后，法官于10时30分宣布休庭。