鄙人做SAT题中语法部分出现一些问题,求英语牛人相助啊!

鄙人做SAT题中语法部分出现一些问题,求英语牛人相助啊!
括号中的部分为原句中的错误部分!
1、Quincy took Dan to Derek's home,for a visit,never imaging that five years would pass (before) seeing Derek again.(08050629)
应改为he saw.但是不明白原句为什么不对,before即可为adv,又可为prep,还可为conj.,为什么这里要用conj而不是prep呢?
2、Determined to make a name for herself as a writer of short stories,Helen never submits anything to an editor until （revising） it several times.（09050625）
应改为Helen has revised.问题和1、类似,until 可为conj和prep,怎么区别呢?
3、(Opposite to) most people I know,Annie,a good photographer herself,actually enjoys seeing the photographs that her friends take on their vacations.（06050626）
应改为Opposite with,但是两者有何区别呢?
4、Chess players find that playing against a computer is helpful (to improve) their skills,even though no chess-playing computer has yet won a championship.（OC010720）
应改为of improving.还是不知道区别.
5、Annual visitors to New York City's Central Park number almost ten times (that of) Mount Rushmore.(07100526)
应改为those to.这道题题意不是很明白,帮忙分析下.
悬赏不是很高,但我也是心有余而力不足啊,

鄙人做SAT题中语法部分出现一些问题,求英语牛人相助啊! 悬赏分：50
括号中的部分为原句中的错误部分!
1、Quincy took Dan to Derek's home, for a visit, never imaging that five years would pass before（ seeing ）Derek again.(08050629)
应改为he saw.但是不明白原句为什么不对,before即可为adv,又可为prep,还可为conj.,为什么这里要用conj而不是prep呢?
答：你括错了.是seeing有错.将同位从句Five years would pass before seeing Derek again提出来看, 这里从句中的主语是five years 而不是Quincy,因此造成see Derek的不是Quincy而是Five years,显然是不对的.
2、Determined to make a name for herself as a writer of short stories, Helen never submits anything to an editor until （revising） it several times.（09050625）
应改为Helen has revised.问题和1、类似,until 可为conj和prep,怎么区别呢?
答：until作介词时,跟时间点如I didn't go to bed until 12 o'clock last night. 不跟doing sth.
作连词时可跟一般过去时或现在时（表将来）untill sth. happened/ happens/ has happened 实际上也是表示一个时间点.
3、(Opposite to) most people I know, Annie, a good photographer herself, actually enjoys seeing the photographs that her friends take on their vacations.（06050626）
应改为Opposite with,但是两者有何区别呢?
答：Opposite to表示“位置、方向’的相反：the houses opposite to ours
不是改为Opposite with, 没这种用法.应改为Unlike
4、Chess players find that playing against a computer is helpful (to improve) their skills, even though no chess-playing computer has yet won a championship.（OC010720）
应改为of improving. 还是不知道区别.
答：be helpful to/ in (doing) sth. 中的to是介词,不说sth. is helpful to do sth. 所以正确答案是to improving
5、Annual visitors to New York City's Central Park number almost ten times (that of) Mount Rushmore.(07100526)
应改为those to.这道题题意不是很明白,帮忙分析下.麻烦了.
答：those to...= the annual visitors to.
句意：每年来纽约中央公园的游客差不多是到拉什莫尔山的十倍.
悬赏不是很高,但我也是心有余而力不足啊,希望高人捧场!

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