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问题 选择题

随着科学的进步，化学与人类健康的关系越来越密切了。下列说法错误的是[ ]

A. 任何有机物对人体健康都有好处

B. 人体内如果缺少铁元素易患缺铁性贫血

C. 处于生长发育期的青少年应多吃富含维生素的水果、蔬菜等

D. 糖、油脂、蛋白质、维生素、无机盐和水都是人类维持生命和健康所必须的营养成分

答案

答案：A

解答题
如果α×
1
4
=b÷
1
4
，a，b均不为0，那么______
A．a＞b B．a＜b C．a是b的16倍 D．b是a的16倍．
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单项选择题

In a public-key cryptosystem, (71) encrypted with the public key can only be deciphered with the private key from the same (72) . Conversely, (71) encrypted with the private key can be decrypted only with the public key. Users can make their public keys (73) available or place them at a key distribution center or others to access. However, the private key must be (74) safe. In public-key systems there’s no (75) to find a safe channel for communicating a shared secret key.

（75）是（）

A.more

B.necessary

C.need

D.space
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