Mark the letter A, B, C, or D to indicate the correct response to each of the following exchanges. Two friends Nam and Lan are talking about the topic of healthy lifestyle and longevity.

Question. Nam: What do you personally do to keep fit? - Lan: ____

A. I think keeping fit is necessary for everyone.

B. As far as I know, more and more people exercise to keep fit.

C. Fitness centres are mushrooming.

D. I just do morning exercise and maintain a balanced diet.