GMAT Sentence Correction (SC) | Re: The results of the company's cost-cutting measures are

In all the first 3 options, where "increased" is used, will it more meaningful if it would have been written as "increased by".
Which one makes more sense:
1. which have increased five percent
2. which have increased by five percent

Or when we say something has increased five percent, "by" is implicitly understood?

I rejected first three options because of this logic. Please explain...