Sentence Correction

Many of today's mathematicians use computers to test cases that are either too time-consuming or involve too many variables to test manually, allowing the exploration of theoretical issues that were impossible to test a generation ago.

1)are either too time-consuming or involve too many variables to test manually, allowing the exploration of
2)either take too much time or involve too many variables to be tested manually; allowing the mathematicians to explore
3)would either take too much time or involve too many variables to test manually, allowing them to explore
4)would either be too time-consuming or would involve too many variables to test manually; this capability allows the mathematicians to explore
5)take too much time or variables to test manually; this capability allows the mathematicians to explore

why is would used here in this sentence...and choice 3 is correct

There is no correct answer for this SC.

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