Which one is correct and why?

A) If the measurements are quantitative (e.g. GPA) and taken from two distinct groups (e.g. Graduate, Undergraduate) the analysis will involve comparing two independent proportions.

B) If the measurements are categorical (e.g. Yes or No to the question "Do you smoke?") and taken from two distinct group (e.g. Female, Male) the analysis will involve comparing two independent means.

C) If the measurements are quantitative (e.g. Weight) and taken twice from each subject observed (e.g. subject's weight before and after dieting)

, the analysis will involve the mean of differences of measurements of each subject.