Both chemical and mechanical digestion start in the mouth and continue in the stomach.

A. Monozygotic; dizygotic: Monozygotic twins are identical twins that result from the division of a single fertilized egg. Dizygotic twins, or fraternal twins, result from the fertilization of two separate eggs.

B. Dizygotic; monozygotic: This is the reverse of the correct order. Dizygotic twins come from two eggs, and monozygotic twins come from one egg.

C. Monozygotic; identical: Monozygotic twins are identical, but this choice does not mention dizygotic twins, which makes it incomplete.

D. Dizygotic; nonidentical: While dizygotic twins are nonidentical, this choice does not properly define the types of twins produced by a single egg (monozygotic).

A. Wastes; nutrients and oxygen: Wastes pass from the fetal blood to the maternal blood, and nutrients and oxygen pass from the maternal blood to the fetal blood.

B. Oxygen and nutrients; wastes: Oxygen and nutrients pass from maternal blood to fetal blood, and wastes pass from fetal blood to maternal blood.

C. Wastes and nutrients; oxygen and carbon dioxide: Nutrients and oxygen pass from maternal to fetal blood, while wastes and carbon dioxide pass from fetal to maternal blood. This option is incorrect because it lists wastes and nutrients incorrectly.

D. Carbon dioxide; nutrients: Carbon dioxide and other wastes pass from fetal to maternal blood, while nutrients pass from maternal to fetal blood.