Nick is admitted to a mental institution because he hears voices talking to him that no one else can hear, and he sees demons attacking him, though no one else could see anything near him. nick's symptoms are known as

Schizophrenia

Explanation:

Those are common symptoms of schizophrenia but it could also be a specific type like "Paranoid Schizophrenic".

so we know the answer cannot be c because no insect or animal starts as an adult

the answer is a. a swimming larvae

because since they are sea animals they automatticaly have to know how to swim they cannot just sink to the bottom

sorry if this is the incorrect answer.