Please explain the meaning of the phrase “US entry was a shot in the arm?”

april 18, 1775, hundreds of british troops marched from boston to nearby concord in order to seize an arms cache.a confrontation on the lexington town green started off the fighting, and soon the british were hastily retreating under intense fire.

on april 19, 1775, american militia gathered to stop a british company sent from boston to capture supplies allegedly amassed in lexington, massachusetts. the militia fled, and the british left after not finding the supplies.

b. parliament was weaker than the monarchy.

b. sec, foreign relations

the answer is prolly b