Explain the relationship between Marginal Cost and Average Cost

Relationship between Marginal Cost (MC) and Average Cost (AC) is stated below:
(i) When AC falls, MC is .lower than AC.
(ii) When AC rises, MC is greater than AC.
(iii) When AC is constant and minimum, MC is equal to AC.
(iv) MC is always to the left of AC and cuts AC from its lowest point.