To combat persistent counterfeiting, Lackland's currency was redesigned to include images that cannot be convincingly duplicated by the means used to successfully counterfeit the old bills. Last year, after the old currency was replaced, many crude counterfeits of the new bills were detected. But now it has been several months since any counterfeit currency has been found. Therefore, it is clear that counterfeiters have largely abandoned their attempt to reproduce the new currency, always assuming that _______.
Which of the following most logically completes the argument?
A. none of the old currency is still in use in Lackland
B. there are no other currencies that can be convincingly duplicated using the old techniques
C. they have not adopted new counterfeiting techniques
D. the penalties for counterfeiting have not increased
E. Lackland's currency is worth more than when the new bills were first introduced
Source: Skills Insight