Answer: c. legal but unethical
Step-by-step explanation:
There is nothing illegal about wanting to back out of a standing commitment to a lender especially if they have bad rates.
It is not considered ethical to do this however because a standing commitment constitutes a promise to do something which means that the other party is expecting that thing to be done. If you then break that promise, the relationship between the person who broke the promise and the affected party will take hit.