Final answer:
Nerve cells would most likely be made as the cells in an embryo's brain begin to differentiate.
Step-by-step explanation:
The cells that would most likely be made as the cells in an embryo's brain begin to differentiate are nerve cells. During the development of an embryo, the process of cellular differentiation leads unspecialized cells to become specialized to carry out distinct functions. Nerve cells, also known as neurons, are responsible for transmitting information and signals within the nervous system, making them the most likely type of cells to be made in the embryo's brain.