This concentration (5 million RBCs per mm3 of blood in an infant) diminishes rapidly in the: reaching a low of approximately 4.1 million per mm3 at what months: The number then increases until:

C.) ... diminishes rapidly in the first month b.) ... reaching a low of approximately 4.1 million per mm3 at 3 to 4 months of age. c.) adolescence, when the adult value of approximately 4.9 million per mm3 is reached.