Which geographic factor enabled the german blitzkrieg to succeed?

The blitzkrieg was the tactics employed by the German Army during World War II.  It use of swift mobility by utilizing ground troops together with armored tanks supported by air power in the skies.  It is through bombardment from both tanks and artillery from the ground to open up enemy defenses supported by fighter planes that would bomb and destroy enemy aircraft on the ground and give support the infantry as the troops moved in to overwhelm the enemy.  Geographical factors that would determine the success of a blitzkrieg would be a flat, open terrain with solid ground with no obstructions.  There are times when rain would be a factor for it would turn the ground into mud making difficult for tanks and trucks to move forward.  Rains and storm also prevent fighter planes to take to the air and provide support to ground forces.  Though in their invasion of France, the Germans successfully managed to cross Ardennes through the forest by chopping the tress , making it easier for their tanks and trucks to pass through.

Iwould say the answer would be b