Final answer:
The four elements of a memo heading are 'to,' 'from,' 'date,' and 'subject,' with a clear subject line that represents the main point and a polite salutation using appropriate titles or honorifics.
Step-by-step explanation:
The four elements of a memo heading are 'to', 'from', 'date', and 'subject'. A clear subject line is crucial as it reflects the main point of the memo, similar to an essay title. When writing, ensure that the subject line is specific enough for recipients to easily refer to it later. Additionally, a polite salutation is important, using the appropriate title or honorific for the individual you are addressing (such as Mr., Ms., Mrs., or Dr.). It's also important to note that in business documents like memos, clarity and specificity help in ensuring that the document is easily understood and that your message is effectively communicated.