Last year, engineers at a local software firm developed a new approach for dealing with increasingly troublesome cyber

This sentence says that engineers at a local software firm developed a new approach to dealing with cyber attacks and this advancement or approach developed has already reduced the attacks by 50%.

Option A - correct
This option is correct because it uses the correct tense of verb which is the present perfect tense, to explain the intended meaning of the sentence.

Option B - incorrect
The past perfect tense of the verb 'had' used with the phrase 'already refused' implies that the attacks were already reduced before the advancement was developed.

Option C - incorrect
The verb tense used is incorrect. It doesn't show the chronological order for the course of action as intended in the sentence.

Option D - incorrect
Adding 'and is' to the sentence is structurally wrong. It functions as a subordinate clause instead of an independent clause.

Option E - incorrect
Although the sentence suggests that there's a development of technology and the advancement reduces cyber attacks. It doesn't show a relationship between new technology and advancement.