The correct option is A Condoms
Condoms are a type of barrier contraceptives. It is a tubular latex sheath that is rolled over an erect male penis prior to sex. This contraceptive device also provides protection from many sexually transmitted diseases.
Spermicides are agents that can kill sperms. Spermicides are available in the market in various forms like jellies, creams, pastes, etc. However, these do not offer protection against STDs.
A diaphragm is a cup-like device that covers the entrance to the uterus to stop the sperms from reaching the egg. Their protection from STDs is very low. Since the mucous membrane of the vagina will still be exposed even after using the diaphragm, there will be a fair chance of sexually transmitted infections to occur.
Cervical caps are smaller forms of diaphragms. They are also fitted to cover the cervix and prevent the sperms from reaching the egg. It is usually used with spermicidal cream or gel. They too are not able to provide adequate protection from STDs.
To ensure the best protection, condoms should be used along with the diaphragms or cervical caps.