Regarding brain development in early childhood, which of the following statements is true?
a. increases in brain size are primarily due to myelination and increases in the number and size of nerve endings.
b. the most rapid period of brain growth throughout the lifespan occurs during early childhood.
c. the prefrontal cortex experiences a growth delay during the process of myelination.
d. there are very few anatomical changes in the brain from ages 3 to 6.

Answer is A. Increases in brain size are primarily due to myelination and increases in the number and size of nerve endings.

Explanation:

Myelination is the process which leads to the formation of myelin sheath around axon or nerve impulse.

The myelin formed is a coating rich in fat, that is found around the axon of neuron. It protects the neuron, and at the same time helps the neuron to conduct signals or impulses move quickly and efficiently.

D. The methyl group of acetyl CoA becomes radio-labeled

Explanation:

During the steps in glycolysis, the carbon at position 1, becomes C-1 in dihydroxyacetone phosphate during the cleavage of fructose-1,6-bisphosphate to dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. Subsequently on isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate, C-1 of dihydroxyacetone phosphate becomes C-3 of glyceraldehyde-3-phosphate.

Furthermore, in pyruvate, the end product of glycolysis, C-3 is converted to a methyl group which then becomes the methyl group in the acetyl-CoA molecule produced from the oxidative decarboxylation of pyruvate.

Since the radioactive 14-C of radio-labeled glucose occupies position 1, it will become the methyl group of acetyl-CoA.