The correct option is B Bacteria
Some bacteria can cause problems resulting in miscarriage. Two in particular - Mycoplasma hominis and Ureaplasma urealyticum. They live in the genital tracts of healthy men and women, but can raise the risk of miscarriage. In women, infection with these bacteria can inflame the endometrium (the lining of the uterus), making it impossible for an embryo to develop, thus leading to abortion. Hence, option B is correct.