Which of These Events Occurs at Rapid Heart Rates

Multiple Choice

Which of these events occurs at rapid heart rates

A) The lengths of systole and diastole shorten equally.
B) The length of systole stays almost constant, but the length of diastole shortens considerably.
C) The length of systole increases at the expense of diastolic time shortening.
D) Diastolic time lengthens, and systolic time shortens.