问题 不定项选择

受东日本大地震影响,福岛核电站损毁严重,泄漏出大量的放射性物质,其中碘-131的危害颇受人们关注。下列关于碘-131的表述中,不正确的是()。

A.有医疗作用,可用于甲状腺功能检查及甲状腺疾病治疗

B.放射性强,碘-131带有强能量射线,可以导致人体DNA发生断裂,并产生一系列的细胞后续反应

C.存在时间久,碘-131半衰期长达8年

D.传播远,碘-131可附着在空气中的尘埃上,向远处扩散

答案

参考答案:C

解析:

碘-131是碘元素的一种放射性同位素,为人工放射性核素(核裂变产物),符号为I-131,半衰期为8.3天。碘-131发射的β射线可杀伤一部分甲状腺细胞,使甲状腺缩小,导致甲状腺合成的甲状腺激素减少,使甲亢表现消失。碘-131带有看不见摸不着的强能量射线,这些射线可以穿过人体组织,穿透过程中遇到阻碍就会与阻碍物质之间形成碰撞并且释放能量。高能量对被碰物质会造成伤害,对人体细胞而言,最直接的伤害就是导致人体的DNA发生断裂,随后产生一系列的后续反应,如细胞表达异常,细胞变性或者坏死,或长时间细胞异化后形成恶性肿瘤。释放出来的碘-131以气溶胶形式存在,可以在大气中漂浮并随大气到处“扩散”。

阅读理解

阅读理解。

      Many Chinese students who have learnt English for more than ten years are still unable to speak English

very well when they meet a foreigner. They seem to have mastered the basic language structure (结构), but

a conversation in English will make them feel uneasy. They are afraid that other people might find out their

mistakes.

      It's uncommon that many students who are bad speakers of English can write English perfectly. This

proves that they are unable to organize their idea in English. The center of the problem is that they lack

practice and confidence (自信).

      Why should you be afraid? Do you fear those foreigners with whom you are speaking? Don't be shy,

they will not laugh at you just for a little mistake you make. The best way to get rid of trouble is to learn to

speak by speaking more. I am sure that constant practice will help you succeed.

1. What's the best topic for the passage? [ ]

A. How to Speak to Foreigners

B. How to Study English Well

C. How to Organize the Idea in English

D. Practise Speaking English All the Time

2. Many Chinese students can write English very well, but they cannot speak English fluently because _____.[ ]

A. they seldom meet foreigners

B. they seldom practise speaking English

C. they had no chance to speak English

D. they think it's enough to master the basic language structure only

3. So many Chinese students are afraid speak to foreigners because _____.[ ]

A. they are afraid they can't understand foreigners

B. they don't think their English is poor

C. they worry about making mistakes in their speaking

D. they didn't tike speaking to foreigners

判断题