Why was the U.S. government's effort to avoid monetary counterfeiting in 1996 met with disappointment? Select one: a. A security thread embedded in the paper failed. b. North Korea purchased the same currency-printing technology that a Swiss company had sold to the U.S. Department of Treasury. c. A watermark including the portrait of the figure on the bill became smudged. d. Microprinting technology made it easy to imitate U.S. currency. e. The optically variable ink was used in smaller denominations only