A Clause That States That a Bank Can Make a Major

A clause that states that a bank can make a major change to the terms of a guarantee as it may see fit and the bank does not have to give notice or get the consent of the guarantor is

A) illegal
B) is legal if the bank gives the guarantor notice of the change but their consent is not needed
C) is legal only if the bank gets the guarantor's consent
D) unenforceable if guarantor has repaid most of the debt already
E) a material variation clause