Can you give us the definitions of those three terms as they are used in your course? And also an idea of the sorts of answers that are expected, for example, by giving us a multiple choice question to give us the general idea?
The FORM of "She used to have long hair." is
A. ....
B. ....
C. ....
And so on. It's so vague, one wants to say, "Well, I think the first sentence is in the form of a pear, the second in the form of a cow, the third in the shape of a jelly-fish!"