Answer:
I used to know this one, so I'm going off of memory and process of elimination.
I'd say it's your financial plan.
A financial plan assesses the ability of the customer to be able to pay back the loan, which is very important to the bank. It also assesses the assets of your business. It's basically showing the bank, how likely is it that we will get our money back from you?
Explanation:
An income statement is improbable because it applies to a company, and typically if you're getting a loan to start a business, you have no income yet.
The bank won't worry about your partnership agreement because that's not related to the fact that you are asking for money to fund your business, they just care that they'll get it back.
A guarantee of success doesn't make sense either because the bank is doesn't need to know if your business will succeed or not, they just want to make sure they get the money they asked for returned at the right date.
