For Endurance Training Such as Walking or Bicycling, Which of the Following

For endurance training such as walking or bicycling, which of the following describes the required exercise intensity?
I.It should be high enough to produce a heart rate greater than 60% of the predicted maximum heart rate.
II.It should be high enough to produce a heart rate less than 80% of the predicted maximum heart rate.
III.It should be high enough to produce a heart rate greater than 40% of the predicted maximum heart rate.
IV.It should be high enough to produce a heart rate less than 60% of the predicted maximum heart rate.

A) I, II
B) III, IV
C) I, III
D) I, IV