What is a preamble (for civics)

What was the difference between bombing military targets in the united kingdom, and bombing the city of london? a. bombing a city kills lots of innocent civilians, bombing a military target doesn't b. bombing military targets didn't force the u.k. to surrender, but bombing london did c. military targets were bombed by japan, while london was bombed by the nazis d. london was bombed before the u.s. entered the war; military targets were bombed afterward