The answer would be C. Energy is used through the food chain so energy always decreases. Population size would commonly decrease according to the pyramid of food chain but since there's no answer for that, C would be the most suitable
Cora might have been diagnosed with another disease that presents similarly as tardive dyskinesia (this disease is a common adverse effect of antipsychotic drugs). Her misdiagnosis is most likely Sydenham's Chorea which affects people with rheumatic fevers. Other differentials include seizures and essential tremors.
The correct terms to fill in the blanks are gastric cavity and extracellular. In cnidarians, the mouth of both the medusa and polyp form opens into an internal gastric cavity where extracellular digestion takes place. The polyp and medusa are body forms that can be found in the phylum Cnidaria. The polyp is a nonmotile body form while the medusa is a free swimming body form.