Which of the following statements is true regarding adolf hitler and joseph stalin's 10-year non-aggression pact?
a. The 10-year non-aggression pact between Adolf Hitler and Joseph Stalin was signed in 1939.

b. The pact included a secret protocol dividing Eastern Europe into spheres of influence for Germany and the Soviet Union.

c. The pact effectively allowed for the invasion and occupation of Poland by both Germany and the Soviet Union.

d. The pact was ultimately broken when Germany invaded the Soviet Union in 1941.