居室装修中经常用到的花岗岩都不同程度地含有放射性元素(含铀、钍等),会释放出α、β、γ射线,这些射线会导致细胞发生癌变及呼吸道疾病.根据有关放射性知识判断下列说法中正确的是( ).
A. α射线是发生α衰变时产生的,生成核与原来的原子核相比,中子数减少了4个
B. β射线是发生β衰变时产生的,生成核与原来的原子核相比,质量数减少了1个
C. γ射线是发生γ衰变时产生的,生成核与原来的原子核相比,中子数减少了1个
D. 在α、β、γ三种射线中,γ射线的穿透能力最强、电离能力最弱
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There is a rule in our school ________ no one is allowed to wear long hair .
A. where
B. which
C. that
D. what
_______last week , she lived a quiet and happy life in that area .
A. Not until the earth - moving machines came
B. The earth - moving machines came
C. Until the earth - moving machines came
D. Then came the earth - moving machines
The young man_______is an engineer from our factory .
A. that you just talked
B. you just talked to
C. whom you just talked
D. you just talked to him
4. Manfred _______from newspaper work to devote his full time to writing .
A. withdrew
B. wandered
C. recovered
D. delayed
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