This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology metabolism, Subject name: Physiology
Separation of first polar body occurs at the time of: 
Select and explain. 
A. Menstruation, B. Ovulation, C. Fertilization, D. Implantation
B: Ovulation
Answer: B: Ovulation 
Explanation: Ans. B OvulationRef: Guyton Physiology, 11th ed. pg. 1027* While still in the ovary, the ovum is in the primary oocyte stage.* Right before it is released from the ovarian follicle, its nucleus divides by meiosis and a first polar body is expelled from the nucleus of the oocyte.* The primary oocyte then becomes the secondary oocyte.* In this process, each of the 23 pairs of chromosomes loses one of its partners, which becomes incorporated in a polar body that is expelled.* This leaves 23 unpaired chromosomes in the secondary oocyte. It is at this time that the ovum, still in the secondary oocyte stage, is ovulated into the abdominal cavity.