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课后练习：
1. This is called background radiation and levels vary from place to place, though the average dose is fairly________.
A. constantB. contactC. contentD. construct
2. While artificial radiation________a small proportion of the total, its effects can be disproportionate.
A. accounts toB. accounts ofC. accounts inD. accounts for
3. It has never been shown that there is ________a thing ________a safe dose of radiation.
A. such; asB. A. such; so C. A. so; asD. A. such; to
4. In general, the effects of radiation can ________those which affect the individuals exposed and those which affect their descendants.
A. be divided inB. be divide intoC. divided into
D. be divided into
5. Some of these are released into the environment, for example iodine and carbon, two common elements ________.
A. used by our bodiesB. be used by our bodies
C. are used by our bodiesD. A. used our bodies
6. Strontium deposits in the bones send radioactivity into the bone marrow, ________the blood cells are formed, causing leukemia.
A. whichB. whereC. thatD. while
7. There are three ________ effects which radiation can have on cells.
A. principalB. principally C. principle
8. In most cases, cell death only becomes ________ when large numbers of cells are killed.
A. significantly B. significant C. abundantD. abundantly
9. Ionizing radiation can damage DNA, the molecule which acts________the cell's "instruction book".
A. inB. outC. asD. toward
10. It may ________increase sufficiently in size to form a detectable cancer.
A. ultimateB. ultimatelyC. ultimacy
11. The fact that the populations ________(bomb survivors, people exposed to nuclear industry) are small.
A. being studiedB. studiedC. be studied
通过本课学习，要重点掌握“非谓语动词”相关语法的内容。简述如下。
非谓语动词包括分词和动名词。
分词的种类：现在分词(the Present Participle)和过去分词(the Past Participle)
分词的作用：主要起形容词和副词作用，在句子中做状语、定语、补语或表语。
分词的区别：现在分词具有主动意义或表动作正在进行；过去分词中及物动词的过去分词具有被动意义，或表动作已完成；而不及物动词的过去分词具有主动意义，如a fallen leaf。
分词的时态和语态：
|
| 主动语态 | 被动语态 |
现在分词 | 一般式 | studying | being studied |
完成式 | having studied | having been studied | |
过去分词 | studied | ||
动名词是具有动作含义的名词，在句子中做主语、宾语或表语；其时态和语态与现在分词相同。
温馨提示：个人认为本课（Radiation and Human Health辐射与人体健康）内容与我们的生活息息相关，而且是科学类的文章，“阅读理解”与“翻译”出题的可能性较大，应认真阅读。
result in结果是…，后面跟的是导致的结果
result from起因于；由…造成，后面跟的是导致的原因
例如：They result in poor capital allocation.它们会导致资本配置不当。
Losses in honey bee populations can result from a number of causes. 蜜蜂群体的损失是由很多原因造成的。
