XDF第5，6套语法题请教

ncraig

1:Only recently ...... possible to separate the components of fragrant substance and to determine their chemical composition.

A:it becomes

B:having become

C:has it become

D:which becomes

不理解选C的原因

2:Although the Earth's chemical composition had been studied for years, only toward the end of the nineteeth centry...... as a discipline in its own right.

A:when geochemistry was recognized

B:was geochemistry recognized

C:then recognized as geochemistry

D:as geochemistry was recognized

这里是否这里不存在as......as的搭配吖？

3The basic) elements of piblic-opinion (research) are interviews, questionnaires, tabulating (equipment), and (to sample) population.

请问Ｄ选项如何改呢？改之后是什么意思？

zhx330330

1.明显的倒装句型。以only 开头的副词、介词短语or状语从句提前至句首时，句子的主要结构倒装。倒装后的句子中的第一个助动词或情态动词位于主语之前，如果谓语是be的一般现在时Or一般过去时，则谓语动词全部位于主语之前。

so c is correct.

2.理由同上。although引导让步状语从句，后面的是主句，这里与as...as 结构没有关系

3。sample->sampling .  这里有and,表示前后的成分作用是一样的。sampling与questionnaires, tabulating 并列。