What causes black holes to form?

How does pregnancy begin? a) a placenta forms in the uterus b) a sperm reaches an egg in the fallopian tubec) the blastocyst differentiates into two cell types d) contractions begin in the uterine wallapex

Why is it important to reduce the number of chromosomes in half when forming gametes for sexual reproduction?

Which feature of a human community is similar to a niche in a biological community