In Return for an Opening of a Second Front Against

In return for an opening of a second front against Nazi Germany in the West in the summer of 1944,Stalin promised at the Tehran Conference

A) peaceful cooperation in the occupation of Germany.
B) to open a front against Japan once Germany had been defeated.
C) to forget about past tensions in Russian-American foreign policy confrontations.
D) to give up parts of his Southeast European colonial possessions.
E) military assistance.