The correct option is D Memorandum
A memorandum is a note recording something for future use, especially business communication with the signatures of the parties concerned. For example, "he told them of his decision in a memorandum". Hence, Option D is correct. Among the rest of the options, agendum means a plan or list of matters to be acted upon, corrigendum means a thing to be corrected, typically an error in a printed book, plagiarism means the practice of taking someone else's work or ideas and passing them off as one's own. These options do not express this meaning, hence incorrect.