How it works ?
For the question displayed, check ALL CHECKBOXES that apply. Then press the CHECK ANSWER button.
If you see nothing, you have not yet answered the question correctly.
If this happens, try to fix your response by checking and/or unchecking necessary checkboxes.
When you’re ready to check your answer again, press CHECK ANSWER.
If you answer this question correctly, you’ll see a big CORRECT! sign appear.
Select NEW PROBLEM to create a new problem.