An extension to file does not extend the time to pay tax. For example, if the tax return is due on April 15 and the taxpayer files an automatic six-month extension until October 15, he or she still must pay at least what percentage of the tax shown on the return when filed or he or she will incur a failure to pay penalty? 

A. 25% 

B. 50% 

C. 75% 

D. 90%