Final answer:
The correct answer is the embryonic period, which represents the stage from the second week until about the eighth week of prenatal development.
Step-by-step explanation:
The period of prenatal development that lasts from the second week until about the eighth week is known as the embryonic period. During this time, significant developments occur, such as the formation of three cell layers, the development of the nervous system, and the initial formation of most organs. This stage follows the germinal stage, and precedes the fetal period, which begins from the ninth week until birth. Therefore, the correct answer to the question is a. Embryonic period.