How does a memo rank in terms of formality of writing style?

A mailing list for e-mail is almost always preferable to sending a separate e-mail to each person.

Which information should not be included in the closing section of a cover letter?

Identify the main attribute(s) of a user-centered objective for a CV/resume.

Fundraising letters should always include a specific date by which you want the recipient to take action.

What is the primary goal of a business memo?

Revising letters and documents is unnecessary as it takes too much time and slows the pace of the business project.

In a business memorandum the letters RE mean Real Executive

In business communications, it is okay to use an abbreviation in the body of the communication if you have spelled out the abbreviation in an earlier place (e.g. People for the Ethical Treatment of Animals (PETA))

In business email communication, it is correct to use such terms as LOL or BTW.

Which of these are ways of using memoranda?