【正确答案】
A
【答案解析】Diction; Rhetorical construction
This sentence aims to emphasize the special prominence of just three specific companies, as opposed to all other companies. Where three most prominent companies is not preceded by a definite article, it is unidiomatic. To indicate that these three were more prominent than any others, it should say the three most prominent companies. If the intention were, instead, to indicate that these companies were merely among a number of highly prominent ones, it should say three of the most prominent companies. Also, in general, one should avoid relative clause constructions when simple adjectives can express the same idea more simply.
A Correct. The three... is used, and prominent modifies the understood companies in a concise way.
B The is omitted before three, and of all the ones that were involved is inferior to a simpler expression such as of all the ones involved.
C The three of them that were most prominent is long and awkward; the three most prominent is shorter and simpler.
D The is omitted before three.
E Not only is the omitted, but three of them that were the most prominent is too long and complex, compared to the three most prominent.
The correct answer is A.