This sentence explains that the proliferation of handguns still continues and that measures enacted at that time to control the proliferation have had only minimal effect.

Option A - correct
This correctly shows parallelism by using 'and,' it also makes use of the correct tense of the verb 'had been' to show that although the action has started in the past and it still continues now.

Option B - incorrect
'only' incorrectly modifies 'at that time' instead of modifying 'minimal effects.' 'It' is very very ambiguous in this question; it is very much preferable to repeat the noun 'the proliferation of handguns.'

Option C - incorrect
Using 'it' in the sentence creates ambiguity. It would be better if the subject 'the proliferation of handguns...' is repeated. Also, 'only' in this sentence seems illogical as it doesn't explain the intended meaning of the sentence.

Option D - incorrect
The report is talking about the proliferation that started in the past and still continues. Whereas, we are looking for the present perfect tense - have had. This option uses the incorrect form of the verb 'had been.'

Option E - incorrect
This has the same issue as option D. In addition, it doesn't show proper parallelism between the proliferation and minimal effects.