"an overwhelming proportion of ..." is a quantity expression. most such expressions, although the words themselves are singular, take grammatically plural forms because they represent quantities that are clearly plural in number.
for instance, percentages, proportions, fractions, and the like fall into this category.
A： note that the construction "that verbed" is just a modifier that modifies the word "act". modifiers are disposable in considering the grammatical structure of a sentence, so you're left with "the act also verbed". that's a complete sentence that is not problematic.
the modifier comma + "making" is illogical, because it would have to modify "was approved on {date x}" -- thus implying that the act made these things happen as a result of the date on which it was ratified. that's nonsense -- these are two different facts about the act, (a) the date when it was ratified and (b) what it actually did.
两个考点
一、
ok Something enables people to hear sounds.
x Something enables sounds to be heard by people.
二、
x Coming home from school, the wind blew me off my bike.
modifier—>who/what was coming home?
Study的主语一定要是人来study
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a就是生活中典型的 我做是对的 你做就是不对的 双规的奇葩