6 Which of the following contributes to genetic variability within a population?
1. genetic drift
II. gene flow
III. mutations
IV. non-random mating
OA. I, II, and Ill only
OB. I, II, III, and IV
OC. I and II only
OD. III and IV only

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]