Need Help

I am doing a web school assignment for my first XML page. I have 3 questions left to complete the assignment on my list, and I do not know how to do, or fully understand. Any clues would be appreciated.
1. an Attribute is used on at least one body element? ...What is a BODY element?

2. Body contains at least one comment documenting each unique element? I know what comments are, and how to put them in a page, I know what elements are, but what is a "Unique Element"?

3. CDATA section used at least once (which I have) but it must "demonstrate the 4 rules", what are the rules?

Thanks

Normally, we don't make a point of doing student's homework here. But I'm going to say this:

The first two questions here (unless we're dealing with XHTML) are very good questions to ask your teacher.

By this, I mean XML doesn't have a good concept of a "body" element or an "unique" element. (HTML and XHTML do have "body" elements, but XML is more generic.) For uniqueness, you might look at DTD's or XML Schemas, but I don't think that's what the test had in mind.