1 Among the （most complex）A cryslals are （that）B of silicon dioxide, which has seven （different）C structures at varjous temperatures and pressures, the most （common being）D quartz.

2 （With more than）A half the world's （annual yield of）B 50 million tons of soy beans, an （important source）C of protein, is （grown in）D the United States.

3. Paleoanthropologists examine fossil （remains）A of extinct primates, while physical anthropologists （concern）B with ethology study the behavior of primates （in）C their （natural settings）D
请说明原因 并分析第3句的结构

1. B 应改为 these，these 是句子的主语，该句是倒装句，谓语动词是are, 主谓要一致。
2. A 应改为 More than， More than half the world's....是主语， 后面的is 是谓语，两个“，”之间的部分是插入语。
3. B 应改为 concern themselves，concern 是及物动词：使关心

Paleoanthropologists（主语） examine（谓语） fossil remains(宾语) of extinct primates, while（连词引出状语） physical anthropologists（状语从句中的主语） concern （状语从句中的谓语）themselves（状语从句中的宾语） with ethology study（介词宾语） the behavior（同位语） of primates in their natural settings.