Which part of speech is the underlined word?

just as i was falling asleep, a moth flew through the open window.

a.
conjunction

b.
preposition

c.
adverb

d.
interjection
through is underlined

b)metaphor

explanation:

when reading the sentence carefully it says,"hope is a thing with feathers" it's like saying: hope is a thing like feathers

get what i'm saying? instead of using a smilie like or as they use "with"

it would be nice enough if i got .

d. therefore pilots wisely train these cubs by various strategic tricks to look danger in the face a little more calmly.

c or d they are the same