无脑选B,虽然犹豫了一下！
It is used in making a "more than" type of comparison where you also want to refer to a previously stated verb / action (that's where the "so" comes in). In this case, the "so" refers to "reported high marital satisfaction."
Notice here that you are comparing two groups of women: those who take new jobs, and those who retire completely. When making a comparison, you have to make sure you explicitly mention both groups.
In fact, B and D change the original meaning of the sentence to make the second part of the comparison a hypothetical - but the original meaning is that the ones who take new jobs are being compared to those who don't.
for comparisons, they two things / groups / whatever compared should be parallel. "women who took" and "those who retired" are parallel.