Amy is a single taxpayer. Her income tax liability in the prior year was $5,178. Amy earns $50,000 of income ratably during the current year and her tax liability is $4,372. In order to avoid penalty, Amy’s smallest amount of required annual withholding and estimated payments is: 

a. $4,372 

b. $3,935 

c. $5,178 

d. $4,660 

e. $5,696