Answer:
by connecting important plot points
Step-by-step explanation:
A Rhyming Couplet refers to two lines of the same length that rhyme and reflects single thought.
The given lines are ''Up rose old Barbara Frietchie then, Bowed with her fourscore years and ten; Bravest of all in Frederick town, She took up the flag the men hauled down''
The rhyming couplets move the action forward by connecting important plot points.