Part of this excerpt would be considered an understatement because

when Cecily says, "There is no reason why I should make a secret of it to you," she actually does have a reason to keep it a secret.

when Cecily says, "Mr. Ernest Worthing and I are engaged to be married," she is actually making a joke.

when Gwendolen says, "I think there must be some slight error," she is actually referring to the large error of Cecily saying she is engaged to Ernest.

when Gwendolen says, "The announcement will appear in the Morning Post on Saturday," she is not telling the truth.

C. when Gwendolen says, "I think there must be some slight error," she is actually referring to the large error of Cecily saying she is engaged to Ernest.