Why is a progesterone-only contraceptive less effective than one containing estrogen and progesterone?

What does homeostasis means in biology?

The allele for curly hair is incompletely dominant. if a mother is homozygous for curly hair and the father is homozygous for straight hair, what percentage of the offspring will exhibit characteristics of both parents? 25 percent 50 percent 75 percent 100 percent

Modern whales developed their traits through natural selection what occurs during the process of natural selection