What world leader signed a secret nonaggression pact with germany

The Neutrality Pact between Nazi Germany and the Soviet Union was signed in Moscow on August 23, 1939. The clause of this pact implied a written guarantee of non-attack of any of the parties to the other, and that no government would unite with someone against the other side of the pact. The pact was officially signed by the foreign ministers of the two countries, but this pact is known as the Hitler-Stalin Pact, so the leader in question is Stalin.

when in doubt choose c

it's what my teacher told my class when we were going into psats

we need the answer choices to answer the question