Which of the Following Is True of Birth Control Pills

Which of the following is true of birth control pills?

A) They prevent ovulation by maintaining consistently high levels of progesterone.
B) They prevent fertilization by changing the chemical makeup of the protective "shell" of the egg so that it cannot be penetrated by sperm.
C) They prevent sperm from entering the uterus.
D) They break down the synchronicity of ovulation and preparation of the uterus so that when the egg is released,the uterus is not at the right stage to receive it.