Which Country where German

pilots underwent on-the-

job training?

The Soviet Union

Explanation:

Because of the defeat in World War I, Germany was forced to sign the Treaty of Versailles. According to the treaty, Germany was forbidden to have any air force and airships and minimum arms and ammunition.  To get training, German pilots secretly trained first in the Soviet Union during the late 1920s for military aviation. Later Germany trained pilots in their own country by covering it under the German Air Sports Association in the early 1930s.

i believe it d) heterogeneous

europe would not recognize the confederacy as an independent nation.