I think is d) (to those who oppose etc...)
B a bee flies sings and stings
The phrase from the excerpt that suggests that Krogstad is prone to engage in crime and may, in fact, be a criminal is the following one:
diseased moral character
It is the only option that talks about somebody being a bad person, which is what Krogstad is. The other options do not show that moral ambiguity this option does.
If you did means it would be past tense. If you do it means you’re doing it in the moment. AKA present tense
