1
What Western European country and its allies have faced off to fight Germany and its allies
twice during the twentieth century?

France is the Western European country that faced off Germany twice during the 20th century.

Explanation:

In the first half of the 20th century Germany was on the rise, industrially, economically, and in militaristic manner. Germany has had expansionist policy and this resulted in wars across the continent. One of the countries that was engaged into military conflict with Germany in both of the World Wars was France.

Being a neighboring country to Germany didn't helped France at all, as the Germans saw it as one of the primary targets. In both occasions the Germans managed to invade France and make huge damage to it, but also on both occasions, with the help of its allies, France managed to push back the Germans and to be victorious over them.

c it says nothing about connecting those 2 seas.