Fertilization in humans is practically feasible only if:-
(1) the sperms are transported into vagina just after
the release of ovum in fallopian tube
(2) the ovum and sperms are transported
simultaneously to ampullary isthmic junction of
the fallopian tube
(3) the ovum and sperms are transported
simultaneously to ampullary - isthmic junction
of the cervix
(4) the sperms are transported into cervix within
48 hrs of release of ovum in uterus