The answer to this question is C. There are a lot of people who know that the various codes can be beneficial for doing specific tasks. In this case, IS NULL is known to be the best option that can be used to check if the value of the column is null or not.
The operator will be in charge of filtering the results based on the details that are provided by the null column value. If in case you do not understand what this means, remember that null has no value. Take note that different constraints may affect the various codes that are available.