I'm thinking it's a or d but i really don't know persia is motivated to show she is more limber on her president's challenge sit and reach test. for the past 6 weeks she has been doing a stretching routine 4 days per week that includes 12 different stretches which she holds for 20 seconds each. a change to her program would indicate she is using the time principle to increase her flexibility when she increases her: holding time to 25 seconds each number of specific core stretch exercises range of motion for each stretch stretching to 5 days per week