6. What must a depositor add to a check before the bank will accept it for deposit?

A. Cancel
B. Void
C. Endorsement
D. Date of deposit

And you think ... ?

C. Endorsement

To answer this question, we need to understand the process of depositing a check at a bank.

When depositing a check, a depositor typically needs to add an endorsement before the bank will accept it for deposit. An endorsement is the depositor's signature on the back of the check which confirms the authenticity of the endorsed check and gives permission to the bank to process the deposit.

So, the correct answer to the question is C. Endorsement.