Final answer:
Option c) Anagen phase is the active growth stage of hair cells, characterized by rapid cell division in the hair matrix that leads to the lengthening of the hair shaft.
Step-by-step explanation:
The active growth stage of hair cells is called the c) Anagen phase.
This is the first phase in the hair growth cycle, where the cells in the hair matrix divide rapidly, contributing to the growth of the hair shaft. The Anagen phase can last for several years and is characterized by the consistent lengthening of the hair. After this phase, the hair enters the Catagen phase, which is a transitional phase marking the end of active growth, followed by the Telogen phase, where the hair is in a resting state. Eventually, new hair cells from the hair matrix will start a new Anagen phase, pushing out the old hair and beginning the cycle anew.