what is the main function of conjunctions?

to modify adjectives
to express feelings
to express an action
to join sentence parts

which sentence use the italicized word incorrectly

the dragon fly skimmed the surface of the pond.
when aunt hazel was young, not girl no would ask a fellow on a date.
the young boy skimmed his knee on the pavement
that fellow is rarely happy. this one

which sentence uses the italicized word correctly?

poems communicate meaning with gestures
the detective force the girl to reveal her secret.
the car's gestures show it was going to stop.
communication is easy when people do not reveal their thoughts.