Final answer:
The correct answer to the question is option B: The militia grew. As the Redcoats marched on to Concord, the American militia retreated but later regrouped and were joined by additional forces. The reinforced militia then employed guerrilla tactics against the Redcoats during their retreat.
Step-by-step explanation:
As the Redcoats marched on to Concord, the initial American militia present in Concord retreated upon seeing the overwhelming British forces.
However, this is not to say they simply fled; instead, Colonel James Barrett decided to withdraw the militia to a nearby hillside to observe the British movements. Subsequently, the American militia was reinforced by additional forces from surrounding towns, swelling their numbers to several hundred, which aligns best with option B: The militia grew.
Additionally, during the British retreat back to Boston, they encountered a guerrilla-style warfare by the American militia and Minutemen, who would shoot from cover and then retreat, constantly harassing the Redcoats along the seventeen-mile march. The British force suffered significantly higher casualties than the colonists as a result of these tactics.