The following lines that best presents the dominant moral of "The Monk's Tale" are:
D. For sure it is, if fortune wills to flee / no man may stay her course or keep his hold
The Monk tale is a series of tragedies which represents the news that the wealth and position is just an illusion. He refers through the example of many falling from high to low end, such as the example of Lucifer falling from heaven. Through such example and stories, he continues to show the people who have fallen from grace.