Expansion into the Soviet Union came later. It was only after Britain seemed to be on the ropes that Germany wanted what the Soviet Union had (oil for one thing). So D is out.
The Soviets had no real ambitions about Germany. It was the other way around. The Soviets had their hands full with the land they had. It's not A.
The Problem is with B and C because both are true. C happened before Hitler came to power. He campaigned on the theme that Germany had to defy the Versailles Treaty.
But that main plank of his campaign would not have been possible without the insistence of Britain and France to pay the reparations in the first place.
I think B is your best answer, but that does not mean that C isn't true.C had to happen before B could. But B was the spark that ignited Hitler's campaign. He made the most of it. They insisted even after Hitler was in power. I think B is your best answer, but don't be surprised to get C. Argue the point and then withdraw.
Answer B <<<< Answer.