Which is the least effective form of birth control

They include injectables (such as Depo-Provera), oral contraceptive pills, patch, ring and the diaphragm. The least effective methods result in 18 or more pregnancies per 100 women in a year, with typical use. They include male and female condoms, withdrawal, sponge, fertility-awareness-based methods, and spermicide.

This is either the spermicidal jelly, or the ring.

Bis the right answer