The Preview allows authors to see how the Item will appear to the student.
Figure 1: Item preview options.
In Item Preview, you have access to the Show Answers button, which will show you the correct answers for each question on the item.
You are also able to check the item is working as expected by seeing the overall score for the item. You can answer each question on the item as a student would, and check that the score correctly reflects the answers you have entered.
Figure 2: Show answer and item score.