Energy would have to be the correct answer
The answer is a cotyledon
Sex cells will always contain half of the number of chromosomes needed for a being. So if a fishes sperm cell contains 12 chromosomes and the ovum also contains 12 chromosomes then when fused together they will have 24 chromosomes in total.
In order for the process of the fish to even be made the sperm and ovum must be fused together. Therefore the number of chromosomes that would be found in the cells forming the gills is 24 chromosomes.
Tape worms have numerous adaptations to enhance their survival in the hosts.
For example the have anatomical adaptations in the form of scolex with hooks that they use to attach to the host small intestine walls therefore preventing them from being excreted following peristalsis. Therefore, the correct answer is that they posses hooks that they use to attach to the small intestines.