The term that refers to the process in which two gametes fuse to make one zygote is called fertilization. Fertilization is the union of male and female gametes (reproductive cells) to produce a zygote (fertilized egg). The correct answer between all the choices given is the third choice or letter C. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.