The large intestine absorbs water, fats, and salts.

A. Ca2+: prevents the entrance of any more sperm- While calcium ions play a role in the slow block to polyspermy, the fast block involves sodium ions.

B. Na+: prevents the entrance of more Na- The fast block to polyspermy involves sodium ions (Na+), but the depolarization of the egg membrane prevents the entrance of more sperm, not just more Na+.

C. Na+: prevents the entrance of Ca2+. The fast block prevents additional sperm from entering, not calcium ions.

D. Na+: prevents the entrance of any more sperm: The fast block to polyspermy involves the opening of sodium ion channels, leading to depolarization of the egg membrane. This depolarization prevents other sperm from binding to and penetrating the egg.

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.