They were exposed to radioactive fallout during nuclear weapons tests.是什么意思？

They were exposed to radioactive fallout during nuclear weapons tests.

在核武器试验中他们暴露在放射性尘埃之下。

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

exposed

adj. 裸露的，暴露的；v. 揭露，暴露；

例句
The biggest fear among parents thinking of using the Internet is that their children will be exposed to pornography...
大多数父母认为使用因特网最可怕的是他们的孩子将接触到色情内容。

to

prep. 向，朝着，到，关于，属于；adv. 朝一个方向的，到某种状态，关闭；

例句
I suggest you leave it to an expert...
我建议你把它留给专家来解决。

radioactive

adj. 放射性的；

例句
Wine is radioactive but few people stop drinking it on that account.
酒是有放射性的，可是很少有人因此而戒酒。

fallout

n. 放射尘，（核爆炸后的）沉降物，附带后果，余波；

例句
They were exposed to radioactive fallout during nuclear weapons tests.
在核武器试验中他们暴露在放射性尘埃之下。

during

prep. 在…的时候，在…期间，当…之时，其间；

例句
...the accrual of funds used during construction.
建设过程中资金的累积

nuclear

adj. 原子核的，原子能的，[细胞]细胞核的；

例句
...members of the advisory committee on the safety of nuclear installations...
核设施安全顾问委员会的成员

weapons

n. 武器，兵器( weapon的名词复数 )，自卫[克敌制胜]的手段[行动]，刀枪，兵戎；

例句
My insurance excludes acts of sabotage and damage done by weapons of war.
我购买的保险对于蓄意损坏以及战争中武器造成的损坏不予赔偿。

tests

n. 试验( test的名词复数 )，考验，测验，化

例句
Strict safety tests are carried out on food additives.
对食品添加剂进行了严格的安全检测。