A March 2000 Census Bureau survey showed that Mexico accounted for more than a quarter of all foreign-born residents of the United States, the largest share for any country to contribute since 1890, when about 30 percent of the country's foreign-born population was from Germany.
the largest share for any country to contribute
the largest share that any country has contributed
which makes it the largest share for any country to contribute
having the largest share to be contributed by any country
having the largest share to have been contributed by any country
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
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