请教几题SAT语法~1.【From】 about 700A.D to 1600,sculptors 【created】

请教几题SAT语法~
1.【From】 about 700A.D to 1600,sculptors 【created】 【nearly】 1000 colossal statues rock on the 【remote】 and tiny Easter Island.答案是no error,为什么created没错?不是应该用had created么?
2.The newspaper business in the United States faces a 【challenge,being that it must reconcile the high-minded goal of informing readers with the commercial one of making money】
答案是：challenge because it must reconcile the high-minded goal of informing readers with the commercial one of making money
为什么不能选 challenge of it reconciling the high-minded goal of informing readers with commercial one of making money?
3.【As】 children mature, they develop 【an independence】 that their parents, who 【have been】 responsible for them since they were born, often find difficult 【to accept】 答案是no error,为什么an independence没错?不是不可数么?
4.【Along】 the curve of islands known as the Florida Keys 【lies】 a reef of living coral,【the only one】 of 【a kind】 in the continental United States.答案是【a kind】 这里a kind 虽然有些别扭 但是具体错在哪里?
5.【If we compare the number of alligators with the Gila monster over time, we see that the alligator is】in decline.
答案是：A comparison over time of the number of alligators and Gila monsters shows that alligators are
为什么不能选：Comparing the number of alligators and the Gila monster, we see that alligators are
6.Unfortunately, the opening of the new library complex, 【previously】【scheduled for】 next September,【would be】delayed for several months 【because of】construction difficulties.答案是【would be】是不是因为要改成will be?那would be 能不能理解成是过去完成时呢?
7.In Germany, foresters discovered that trees killed by acid rain had begun to die four years 【earlier, even though the trees had shown no signs of disease then.】
答案是选原句,为什么不能选【earlier without any signs of disease shown then.】?我觉得这个更简洁而且没什么错..