What is the primary mechanism of action for the contraceptive sponge?

The correct choice identifies the primary action of the contraceptive sponge as killing sperm and creating a barrier. The sponge is made from polyurethane foam, which is designed to not only physically block sperm from entering the cervical canal but also to contain a spermicide, typically nonoxynol-9. The spermicide is effective in incapacitating sperm, thereby preventing fertilization.

This dual action—mechanical barrier and chemical action—allows the sponge to serve as an effective method of contraception. By blocking the sperm's path and neutralizing its ability to fertilize an egg, the sponge helps to significantly reduce the likelihood of pregnancy when used correctly.