During fasting or starvation, the brain:
a) converts endogenous fatty acids into β-hydroxybutyrate.
b) utilizes β-hydroxybutyrate from the blood stream.
c) utilizes amino acids for fuel from degradation of brain protein.
d) utilizes its glycogen stores as a first responding source of fuel.
e) all of the above.

Utilizes its glycogen stores as a first responding source of fuel.

Explanation: The brain only uses glucose as source of energy. When there is too much blood glucose, insulin is activated and anabolically starts the proces of gluconeogenesis, where glucose is stored in branches. During starvation these glucose molecules are broken down catabolically to provide the brain fuel or energy.