1. Stars shine because of _______ produced by the nuclear reactions taking place within them.
解析：because of 是介词短语，后面要跟名词性短语
(A) the amount of light and heat is 是句子，语法错误；
(D) the amount of light and heat 名词短语，符合要求。
19. 句子中的with exploring areas unknown to them and（改为about）describing distinctive features of individual places.是并列关系，分解如下：
1. Geographers were once concerned largely with exploring areas unknown to them,（be concerned with 参与到…）理学者曾经主要参与到勘探他们未知的地区。
2. and they were concerned about describing distinctive features of individual places（e concerned about 关心…），他们对描述个别地区的独特地貌表示关心。
21. The first city in the United States that put into effect major (改为 to plan) for the clustering of government buildings was Washington, D.C.
拆分：
主句：The first city in the United States was Washington, D.C. 美国第一个城市是华盛顿特区
定语从句：that put into effect major to plan for the clustering of government buildings主要是为计划聚集政府大楼开始实施的（城市）
其中to plan for doing是目的状语
35. Physicians working in the field of public health are mainly concerned with the environmental causes of （改为illness） and how to eliminate them.
1. 本题中的 be concerned with 意思同第21题，表示“参与”，即：供职于公共卫生的医务工作者主要参与 ... 环境事业。
2. ill是形容词，不能用作介词宾语，应该改为名词illness
38. Astronomers use photography and sighting telescopes to study the motions of all of
the bright stars and many of the faint ones.
两个of的作用不同，第二个all of 和many of 是名词短语，作第一个of的宾语，修饰motions
1. the motions of …的运动
2. all of the bright stars and many of the faint ones：所有明亮的星体和多数昏暗的星体
3. 合在一起：所有的明亮的星体和多数昏暗的星体的运动
国内英语考试，真不是盖的~sorry mate, I have no idea~
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