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
I'm pretty sure it's a dependent clause. Hope this helps!
The word <em>quickly </em>describes the verb, or the way in which the line is moving. This means that this word is an B. adverb.
A would be - is long, is moving
C would be - long
There are no prepositions here.
