They are helping verbs. Your helping verbs are the following:
am been may
is can might
are could must
was shall
were should
be will
being would
A third person narrator knows all the characters' feelings and thoughts, an author might choose this perspective to let the reader know everything the characters are feeling and what's going on. This gives a broader perspective on the story and can influence the readers opnion.
Answer:
D. is the answer of the question
Large is an Adjective
Fish is a Noun
Swim is a Verb
Swiftly is an Adverb
In is a preposition
The is a determiner
Sea is a noun.
I hope this helps since you didn't say which word is italicized.