The correct option is A to prevent the sperm from coming in contact with the ovum
Vaginal diaphragm is one of the barrier methods of contraception for females. Diaphragm is placed over the cervix to prevent the entry of sperms into the uterus. This prevents the sperms from coming in contact with the ovum.
A diaphragm is a rubber, dome-shaped device which can stop the sperm-entry, but cannot kill them (no spermicidal action) on its own. But, spermicindal creams can be applied to the diaphragm in order to kill the sperms.
Ovulation (release of secondary oocyte into the fallopian tube by the ovary) and implantation (attachment of developing embryo to the wall of uterus) takes place inside the female reproductive tract. These physiological processes cannot be prevented by using external barrier methods.