Timothy, a cashier, is given a twenty-dollar bill at his store. he is suspicious of the customer and wants to make sure the currency is real. which would be a clue that the currency is counterfeit?
there are watermarks in the paper bill.

there is a security thread in the paper bill.

there is no gold standard backing the bill.

there is no change in the color of the bill's ink.

There is no change in the color of the bill's ink.

Explanation:

There are several methods to check if the currency is counterfeit apart from all the lab related approaches, one can do a preliminary check to see if the currency is counterfeit or not.

One such method is to check if there is any color change in the bill's ink, in case there is a color change then the currency is not counterfeit. A counterfeit currency will have not color change of the bill's ink.