TirthankarP
A report recently released by the Public Safety Commission confirms that the proliferation of handguns among minors, which was noticed five years ago, still continues and
that measures enacted at that time to control the proliferation have had only minimal effect.
A) that measures enacted at that time to control the proliferation have had only minimal effect
B) that measures enacted to control it at that time only have had minimal effect
C) that measures enacted to control it at that time have had a minimal effect only
D) measures enacted at that time to control it had been only minimally effective
E) measures enacted to control the proliferation at that time were only minimally effective
This question is pretty full of nice eliminations: Parallelism, Pronouns, Modifiers, Verb Tense...
Parallelism: The parallel marker (signal) is the word "and" and the two parallel elements start after "confirm" and are 1) that the proliferation... and 2) that measures... (I personally would have like to see the word the as well "that THE measures"). D & E don't have proper parallelism.
Pronouns: "It" is very ambiguous on this question (the GMAT is tolerant of reasonable ambiguity), and we are given a choice between an ambiguous pronoun and a clear, repeated noun, so we will eliminate the ambiguous pronoun in B, C & D.
Modifiers: "Only" needs to modify the minimal effects. In B, "only" incorrectly modifies "at that time" and the "only" in C is awkward and doesn't convey the same meaning as the original.
Verb Tense: Because the report is talking about the proliferation that started in the past and still continues we are looking for the present perfect tense - have had. D & E do not have the proper verb tense.
Plenty of reasons to stick with the original on this one

KW