Answer:
Option A, Isogametes
Step-by-step explanation:
Unicellular organism mostly reproduce asexually and hence the offspring formed are exactly same to the parent cell in all respects. An isogametes produces gametes which have same size and structure as that of parents cell. While an anisogametes differ in size and structure as the male gamete is smaller and motile as compared to the female gamete.
An oogametes is specifically a large female gamete.
Hence, option A is correct