The correct option is C Polyp
Hydra belongs to the Hydrozoa.
Many members of the Hydrozoa go through a body change from a polyp to an adult form called as medusa. However, all Hydra, despite being hydrozoans remain as polyps throughout their lives.
So, any form of phase is completed by polyp, be it nutritive, digestive or sexual phase.
Therefore, the correct answer is option A.