Which of the following group functions ignore NULL values?

Answer: Option D

All three of the listed SQL group functions, MAX, COUNT, and SUM, have the ability to ignore NULL values when processing data within their respective functions. Here's a brief explanation of each option:

Option A: MAX
The MAX function is used to find the maximum (largest) value in a set of values. It can operate on a column and will return the maximum value, ignoring NULL values in that column.

Option B: COUNT
The COUNT function is used to count the number of rows in a result-set or the number of non-NULL values in a specific column. It ignores NULL values when counting.

Option C: SUM
The SUM function is used to calculate the sum of all values in a numeric column. It adds up all the non-NULL values and produces a result, ignoring NULL values.

Option D: All of the above
This option is correct because all of the mentioned group functions (MAX, COUNT, and SUM) have the capability to ignore NULL values when performing their respective operations.

So, the correct answer is Option D: All of the above.