The mitotic division starts as the zygote moves through the _____ of the oviduct called cleavage.

The correct option is C Isthmus
The process of fusion of a sperm with an ovum is called fertilisation.
The mitotic division starts as the zygote moves through the isthmus of the oviduct called cleavage towards the uterus and forms 2, 4, 8, 16 daughter cells called blastomeres.

So, the correct answer is-option b.