The major body of the essay should be 3 or 4 paragraphs long for a 20-point exam, and 4 or 5 paragraphs long for a 30-point test, with 4 or 5 points coming from both the item you were given and your own expertise. You should not write more than one paragraph on any single subject. There are no specific words or phrases that would indicate to the examiner that you are using points from the exam to calculate your score. It is simply assumed that if you get more than one item right, then you must be using your own knowledge to help you achieve a high score. As with all academic essays, the quality of your work will be seen through its clarity in explaining ideas and facts as well as its elegance in writing style. So make sure that you take time to edit your work before you submit it.