Choose the best response by clicking on it. If one of the answers is followed by 'Either is correct' in parentheses, and you think that is correct, choose that one. It is the best answer.
The timer gives you 15 seconds to find the answer. It notes your errors but it only shows you the correct answers at the end.
If you don't use the timer you see the correct answers immediately and in many quizzes you can click on Another example to see a similar word or sentence.