In the Listening Test you have 10 minutes at the end of the test to transfer your answers to the Listening Answer Sheet, so just write directly on the question booklet so you can fully focus on the listening .Then check grammar and spelling at that time However, in the Reading Test, there is no transfer time, so when you are sure of an answer, write it on your answer sheet. That way, if you run out of time, most of your answers will be on the Answer Sheet
