Simplify the following text for a Grade 3 native English-speaking person.
Original: Though Mozart touched on various minor keys in his symphonies , G minor is the only minor key he used as a main key for his numbered symphonies ( No. 25 , and the famous No. 40 ) .
Simplified: G minor is the only minor key he used as a main key for his numbered symphonies ( No. 25 , and the famous No. 40 ) .