What should you remember to do if you are returning the car to an airport?
Remember to ________ to check in to your flight.
leave enough time
（题目在问如果你把车送回机场， 你应该记得做什么。 根据原文“ if you are returning the car to an airport, remember to leave enough time to check in to your flight.” 可知， 如果你要把车送回机场， 记得留出足够的时间办理登机手续。 结合提示， 此处填写 leave enough time。）