A"check", the form most routine maintenance (on aircraft) takes, comes is several grades, referred to as "letter checks" a through d; all performed at regular intervals. which of the following four hour intervals, representing a, b, c, and d are correct?

125; 750; 5,000; 20,000

100; 500; 5,000; 25,000

125; 750; 3,000; 20,000

100; 500; 3,000; 25,000