Plagiarism may be:

a. committed unintentionally
b. the result of ignorance of the offense
c. committed intentionally
d. all of the above

The correct answer is D: all of the above.

Plagiarism is the taking of information without properly crediting the source. This is seen as stealing information and can result in a poor grade on any paper/assignment.

Plagiarism can be committed unintentionally, such as quoting an author of a book and forgetting to credit him/her. 
It can also be committed intentionally, such as stealing information in order to save yourself time from writing it in your own words. 
Lastly, plagiarism can be committed out of ignorance. This means that the person is unaware that he/she needs to credit the source of the information used.
These are all examples of how plagiarism may be committed.