Why did the soviets not allow people to leave occupied east germany

Its been a while since I did this topic, but I believe it was mostly because under communism there was little work for intellectuals, so they were often the ones who left the country. This resulted in a 'brain drain', a lack of knowledgable people. I seem to remember reading about the entire maths department of a university just up and leaving at one point. You could also argue that it was damaging for the image of communism if so many people were trying to leave.

Ithink it would be choices a and b. hope this !