This center part is not present in everyone's hair or may be broken into segments. a
Medulla
b
Cortex
c
Cuticle
d
Keratin

C. Cuticle

Explanation:

Cuticle is the correct answer for this question

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.