The correct option is C Diaphragm
Mechanical barriers of contraception
Mechanical or barrier methods are those methods of contraception which prevent physical meeting of ovum and sperm.
Diaphragm
Diaphragms are introduced in the vagina to cover the cervical region of the female reproductive tract to prevent the physical meeting of gametes (egg and sperm).
Therefore, diaphragms are mechanical/barrier methods of birth control.