Answer
(b) an experiment, but not a double-blind experiment
Work Step by Step
An experiment deliberately imposes some treatment on individuals in order to observe their responses.
A double-blind experiment is one in which neither the subjects nor the individuals who measure know which treatment was received.
A matched pairs experiment compares two treatments which each subject undergoes.
An observational study tries to gather information without disturbing the scene they are observing.
EXPERIMENT, because the treatments are cardiovascular training or strength training.
Not a matched-pairs experiment because the people in the two treatment groups are unrelated.
Not a double-blind experiment because the subjects are aware of which training they receive.
