Which of the following best describes when a person is ready to move to stage II cardiorespiratory training from stage I?
a. Client can maintain a zone 1 heart rate for 20 minutes.
b. Client can maintain a zone 1 heart rate for 30 minutes.
c. Client can maintain a zone 1 heart rate for 15 minutes.
d. Client can maintain a zone 1 heart rate for 10 minutes.