The
increase in the number and scope of investigations into monopolistic business practices, in addition to the expansion of definitions of such practices, have resulted in more antimonopoly litigation presently than ever before.
The increase in x in addition to xxx , has resulted -> The subject of the sentence increase is Singular so A and D are wrong
(B) has resulted in greater antimonopoly litigation presently than previously -> We can count the number of litigations but ligation itself isn't a number hence we do not use greater than here
Some examples of nouns that are themselves numbers are: percent, interest rate, population, volume, distance, price, cost, and number.
(C) has resulted in more antimonopoly litigation
at present than was seen ever before (X than was xxx ) - Not parallel
(E) has resulted in more antimonopoly litigation at present than ever before - No errors and concise