Why do we need to enclose in quotation marks (“ ”) the string values? (in Excel spreadsheet) =IF(E4="ELIGIBLE FOR INCENTIVE", D4*4%, 0)

a. We need to enclose in quotation marks the string values to avoid error.
b. We need to do that because it is required in the formula that has IF function.
c. We need to do it because the string values need to be recognized as strings
and not numbers or variable names.
d. We need to enclose the strings in quotation marks so that everything in the
formula with an IF function is in place.