C.
Biotic mean alive, so we can cut off the first 2 easily. Aquatic birds eat frogs, so that one is safe for now. A decrease in something parasitic usually helps the population, so D is out too. The only one left is C.
Plants gain energy from the sun light to help preform photosynthesis
The best answer would be:
Unconditioned stimulus
In Pavlov's experiment on conditioning the food was the unconditioned stimulus that triggers a reflex or natural behavior. Think of it like something that makes you do something automatically.
For example, the food. When the dog smells food, it salivates. This is unconditioned because without teaching the dog, it automatically responds by salivating.
Answer:
I believe intestine.
Explanation:
since tapeworms resides in intestine
