For a (say) 8 marks question in assignment X3, I could only come up with 3 sentences! And the solution gave like 50 sentences! So depressing ..
So what are you missing? Study the solution carefully. What was the descriptive word in the sentence eg Describe, state, list etc. That gives the level of detail you need. It sounds as if you are getting the main thread but lack expansion. Its all about exam technique. So don't get down, get down to some more practise! And remember, the best answers are those that are succinct. You don't have to write 8 pages for 8 marks (but generally more than 3 sentences)