Hello. You did not show the results of the study to which this question refers, which makes it impossible for it to be answered accurately. However, I will try to help you in the best possible way.
Antibiotics that were most effective in overcoming bacterial resistance and killing a large number of bacterial colonies, if not all, should be chosen. In that case, antibiotics are chosen where the bacteria are more susceptible and fragile. In relation to bacteria B. subtilis, the antibiotics clindamycin and vancomycin, tend to be more efficient.
Antonym for earlier:later, or next.
Provide reasoning is the next best thing to do if the person is writing and argumentative prompt.
I think B. But instead of those dots, I prefer a comma instead
I think present particpile