Ron神解释的是，since一定要和had或者has连接在一起！！！所以答案b，has……since

DE中用不定式代表的语义不合适？

B the largest share that any country has contributed做accounted for的内容的宾语
since要带完成时

having 的逻辑主语是mexican 他们自己就是share的一部分 怎么能够自己having 自己呢

这道题为什么要用同位语而不是用伴随状语？having the largest share to have been contributed by any country也可以修饰accounted for呀？还有A和B的区别除了时态（since 1990是完成时的标志），还有to contribute意思目的是去贡献什么，但是这里只是说任意国家贡献最大的一部分？

这道题为什么要用同位语而不是用伴随状语？having the largest share to have been contributed by any country也可以修饰accounted for呀？

补充：B. Correct. This form of the appositive is the most efficient way
to express the comparison. Depending on when the sentence
was written and what the writer intended to express, the verb
form could be either had contributed or has contributed. The
use of has contributed implies that, from the perspective of
the sentence, the comparison between German-born U.S.
residents and those from other countries still holds true.

①有的时候同位语可以很简洁明了的表达含义
②since一定得加完成时态（要从全局出发把握时态），现在完成时
③DE中have的修饰是to do sth很不合理；to do通常表示一定的purpose
I lifted the weight to free my leg.

having 感觉和前面指代 不明吧

AB均为同位语／从句，其中B的完成时态，符合文中since +年份的要求；C定语从句的关系代词which和代词it冗杂；DE现在分词造成冗杂

考察定语和同位语的区别，明显the largest share应该做more than a quarter 的同位语

B. Correct. This form of the appositive is the most efficient way to express the
comparison. Depending on when the sentence was written and what the writer
intended to express, the verb form could be either had contributed or has
contributed. The use of has contributed implies that, from the perspective of the
sentence, the comparison between German-born U.S. residents and those from
other countries still holds true.

A. The phrase for any country to contribute makes the sentence wordy and indirect.

A：for any country to contribute是share的定语
B： that any country has contributed也是share的定语
无成分差异，考虑外延与内涵，从句和不定式的区别，定语成分考虑主句的约束力，主句的发生不能导致变化部分的发生，即墨西哥占了多少百分比与其他国家没有关系，不能用不定式。