The unemployment rate may underestimate the true extent of unemployment if:
a. many part-time employees would like to work fulltime, but are unable to get the additional work.
b. employees increase the number of hours they work overtime.
c. there are a large number of people working in the underground economy.
d. people are pretending to look for work so that they can continue receiving unemployment benefits.

c.

Explanation: The unemployment rate may underestimate the true extent of unemployment if there are a large number of people working in the underground economy . While the underground economy also known as the black economy may conjure up images of drug deals and prostitution rings, the term actually has much broader scope. It refers not only to illegal economic activity, but all economic activity that goes unreported to government authorities and consequently, avoids being taxed. one of the primary reasons the underground economy exists is that people are trying to evade taxes. But increased government regulations that can make the cost of doing business higher also create an incentive to avoid reporting certain economic activity to the government. An increase in the number of unemployed increases the number of people who work in the black economy because they have more time. On the other hand, an increase in unemployment implies a decrease in the shadow economy.