What should I add to my paper on the Auschwitz Gate to make it longer?

Certainly, there was a lot of cruelty in all of the camps and I am sure you could expand that topic by at least one paragraph to reach your goal. It is hard to tell...is Zyclon B the only thing you talk about in that section? Didn't the Nazi's also murder the prisoners in different ways? (For example, through firing squads?) If so, you could add information about that. If your paragraph 5 is about more than just the gas, just add another means or two by which the cruelty was enacted.