a, How often do Mai and Phong go swimming ?
---> Mai and Phong go swimming once a week.
b, How often do you visit your grandparents ?
---> I visit my grandparents once a week
c, How often does your sister brush her teeth ?
---> My sister brushes her teeth twice a week
d, How often do they skate ?
---> They skate twice a week
e, How often do your father do exercise ?
---> My father does exercise every morning