Aunicellular sexual ciliate has seven different mating types that produce gametes of roughly the same size. any gamete from any given mating type can fuse with any other gamete, except for one of its own mating type. these ciliates therefore exhibit

I believe that these ciliates therefore exhibit what we call isogamy.  This is a type of sexual reproduction which involves gametes of similar morphology, meaning the size and shape are similar, differing in the allele expression in one or more mating type regions. Now it is because of this fact that the gamates look alike and thus, they can not be classified as male or female. 

According to edgenuity, the answer is c.