The correct option is C given an injection of thyroxine
The thyroid gland produces thyroxine. Thyroxine is responsible for metamorphosis in frogs. Metamorphosis is a developmental process wherein a larva develops into an adult. In the absence of thyroxine, metamorphosis will not occur in frogs i.e. tadpoles will not develop into frogs. However, an injection of thyroxine will bring about metamorphosis.
Growth hormone and oxytocin have no role in metamorphosis in tadpoles; therefore injecting them will not help.