The right option is; orbital period
T stands for orbital period.
Orbital period is the time a certain astronomical object such as planets takes to complete one orbit (360° revolution) around another object such as sun or stars. Orbital period is expressed in different units of time, usually in years, days or hours.
The testes is where you will find them
Answer -
T-Cell - White blood cell = Fight off Intruders in the body
B-Cell - Macrophages = Creates Antibodies against antigen.
Cell Differentiate - Stem Cells = My favorite cell of all time in animal because they can turn into almost any cell like neural, signaling, euthyroid. Etc