I was in health last year, but i think i remember.
Muscular endurance is the ability to endure for a long time.
Lifting weights builds more on size. "Size is the prize, swole is the goal"
Stretching only stretches muscles so you dont pull them.
Sit-ups is also for size, or looks. It builds the abs.
Cycling builds muscular endurance in the legs.
Cycling is your answer.
-Seth