The War Fought in Spain Was Significant Because It

The war fought in Spain was significant because it:

A) proved once and for all the invincibility of Napoleon's battlefield tactics.
B) indicated that Napoleon could be defeated on the battlefield.
C) finally allowed Spain and Portugal to be reunified into a single country.
D) was the means to forge the Fourth Coalition to finally defeat Napoleon.
E) showed the superiority of French rifles and artillery over that of the Spanish.