What was the significance of the Gothic Line?

A)It was a set of fortifications in Italy that gave the Allies the upper hand when they broke through to wrest control of northern Italy from the Axis.
B)It was a line of convoy trucks that supplied the Allies as they attempted to take Italy from Axis control.
C)It was a naval blockade around Great Britain that protected Allied shipping from Nazi submarine attacks
D)It was the system of coastal defensive structures built by the Nazis in northern France that kept the Allies from invading.