To answer the first part of your question, I'd like to say that our studies were very extensive.
你问题的第一部分,我要说的就是我们的研究非常广泛。
It's about a time when there were black slaves in North America. It's about their fight for freedom.
(它)讲的是有一段时期,北美洲存在黑奴。影片讲述他们为自由而斗争的情况。