Concept:The series follows an increasing number of letters in each word.Explanation:Count the letters in each given word:win = 3 lettersnote = 4 lettersgrain = 5 lettersbroker = 6 lettersSo, the next word must have 7 letters.Check the options:refund = 6 letterspony = 4 lettersbanking = 7 lettersmutually = 8 lettersThus, banking completes the pattern.Answer:banking