Which of the following is an example of a character function in SAS?

The selection of the character function UPCASE is accurate because it is specifically designed to manipulate character strings in SAS. The UPCASE function takes a character value as input and converts all the letters in that string to uppercase. This is particularly useful when there is a need for standardization of text data, such as ensuring consistency in case for comparisons or outputs.

On the other hand, the functions mentioned in the other options serve different purposes. SUM is an arithmetic function used to add up numeric values, while TRUNC is a numeric function that can be used to truncate a number to a specified number of decimal places, primarily dealing with numeric data rather than character strings. AAVG is not a standard function in SAS and appears to be a typographical error, possibly intended to refer to AVG, which is also a numeric function for calculating averages.

Therefore, the correct answer stands out because it is the only option focused on character data manipulation within SAS.