Final Answer:
The error message when you attempt to use a cell that has been deleted as a function argument is #REF! (Option C).
Step-by-step explanation:
In Excel, the #REF! error occurs when a reference is not valid, often due to deleted cells or ranges. If you use a cell that has been deleted as an argument for a function, Excel cannot find the reference, resulting in the #REF! error. This error indicates a problem with the cell reference and signals that the formula or function cannot perform the intended calculation due to the missing or deleted reference. Options #NPV?, #NAME?, and #N/A do not specifically relate to referencing errors but rather to issues with net present value, undefined names, and unavailable values, respectively.
Option C is the answer.