Fact Pattern 33-1Petro Oil Refinery Asks Quality Bank for a Loan

Fact Pattern 33-1Petro Oil Refinery asks Quality Bank for a loan to increase its oil inventory. Quality requires Robin, Petro's president, sign a personal guaranty to pay the debt if Petro defaults. Meanwhile, to sell fifty barrels of refined oil to Slick Lubricants, Inc., Petro asks its outside accountant Tina to co-sign a credit application.
-Refer to Fact Pattern 33-1.If,after the loan agreement is signed,Slick agrees to a higher rate of interest without telling Tina,then Tina is 

A)  ​discharged from the agreement. 
B)  ​liable at the higher rate of interest. 
C)  ​liable at the lower rate of interest. 
D)  ​liable for the principal only.