Let's hear it for A. "Dwindle" implies a gradual lessening of something and applies to things growing visibly smaller. ("The size of the speaker's audience gradually dwindled.") "Diminish" emphasizes a noticeable loss and implies a subtraction from a total. ("Our dog's sense of smell diminished with age.") Another synonym, "decrease," suggests a progressive decline in size, amount, numbers, or intensity. ("The researcher slowly decreased the amount of weight.") "Lessen," meanwhile, implies a decline in amount rather than number. ("The young couple tried to lessen their debt.") Lastly, "abate" indicates a reducing of something oppressive or excessive in force or amount. ("After several scorching days, the heat abated.")