Explain "Meiosis 2 completed only at the time of sperm entry."
Primary oocytes are formed prenatally and remain suspended in prophase of meiosis I for years until the onset of puberty. An oocyte completes meiosis I as its follicle matures (during ovulation) resulting in a secondary oocyte and the FIRST polar body. After ovulation, each oocyte continues to metaphase of meiosis II. Meiosis II is completed only if fertilization occurs, resulting in a fertilized mature ovum and the second polar body.
So in short, the egg is stuck in metaphase II until fertilization.