Marissa's target heart rate zone is 140-178. during a tennis match, she checks her wrist monitor, which indicates that her heart rate is currently 130. which of the following will her get the most productive workout, based on the information she has gathered?
a. moving more quickly and serving the ball with greater intensity
b. moving more slowly and serving the ball with less intensity
c. deliberately trading points to change the duration of the match
d. deliberately shortening the duration of the match to play less