The correct answer is D.
N/A is a common abbreviation and it stands for<em> not applicable, not available,</em> <em>no answer.</em>
It is used to indicate when certain piece of information is not provided, either because it does not apply to a particular case in question or because the answer is not available.
The usage of N/A dates back to the year 1920.
The N/A abbreviation is used to distinguish a blank space that can not be filled due to lack of information and it is not left blank erroneously.
