谁能帮帮忙！翻译一下！
Jack is in the vocative case because someone is speaking to him. (But we could say that Jack is in the NOMINATIVE case because he is the subject of the sentence and thus we could do away with the need for a vocative case here!)
You is the nominative case because it is the subject of the sentence (but Jack can also be regarded as the subject of the sentence because Jack and You are the same person! If I said, "MY NAME IS FRANK" the word Name and the word Frank refer to the same person and I could equally well have said "FRANK IS MY NAME" ie (short for THAT IS) the two sentences mean much the same.)
Robert is in the ACCUSATIVE case because it is said to be governed by the preposition
AGAINST.
参考答案:Jack是呼格，因为别人在跟他说话。（但我们可以说Jack是主格因为他是句子的主语，因此我们这里可以不需要一个呼格）
You是主格因为它是句子的主语（但是Jack也可以被认为是句子的主语因为Jack和You是同一个人！如果我说：“我的名字是Frank”，Name和Frank两个词都指同一个人，而我可以同样说“Frank是我的名字”，也就是说两句句子的意思是一样的（ie是That is的略词））
Robert是在宾格因为它是由介词against所修饰的。
（你是在学什么阿，怎么那么多英语词汇语法……）