Which of the following are required for fertilization to occur inside the female body?
a sperm must swim into an oviduct.
b an oocyte must be present in the oviduct.
c the nucleus of a sperm must fuse with an oocyte nucleus.
d all of these

d all of these

Fertilization is where the egg cell of the females meet the sperm cell of the males, Further it is even a step by step process, stated in the provided options.
Considering that the female and male sex cells are present
1. Sperm must swim into an oviduct.
2. b An oocyte must be present in the oviduct.
3. c The nucleus of a sperm must fuse with an oocyte nucleus.