The accompanying diagram shows the uterine tubes of four women (P, Q, R and S):
In which two women is fertilization impossible at present?
(1) P and Q
(2) Q and R
(3) R and S
(4) S and P
(3) Fertilisation in human females takes place at ampullary-isthmic junction.
P: Partial blockage in both fallopian tubes, so it would not affect the mobility of gametes and thus fertilisation can take place.
Q: One fallopian tube is completely blocked but fertilisation can easily take place in the unblocked fallopian tube.
R: Both of the fallopian tubes are completely blocked, hence no fertilisation.
S: Tubectomy has been done which is irreversible thus fertilisation is impossible in this case.