Paula Kuchinski, a well-known investor in the New York area, has been returning substantial profits for her clients over the past 10 years. With a recent decline in the stock market and trading, the returns have ceased to exist. Phone calls to Ms. Kuchinski, from clients looking to remove their investments before the market crashes, are not being returned. Ms. Kuchinski is believed to be involved in what type of scheme when investment fraud occurs that involves the payment of purported returns to existing investors from funds contributed by new investors?

a. trickle down
b. Sutherland
c. market
d. Ponzi
e. Madoff