A- if a drug is given that makes the patients BP more variable, then the resulting CI of the post-treatment BP will be wider.

B-A 90% CI of the BP based on the same data will be narrower.

C-If a drug is given to exactly reduce the BP by 10 units in every patient, then the CI post Treatment will be narrower.

D-A 95% CI on a random subset of 60 patients is going to be wider.

I'm having trouble wrapping my head around this problem. I thought the answer was C, but now I'm questioning myself. Any thoughtS??