Hi!
The correct option would be D. All of the above
Emails are the most commonly employed form of correspondence in the business world. They are kept very clear and concise in the business sector because of the formality and seriousness of the communication. Emoticons are not recommended because they can be misleading, and one can interpret them incorrectly -which is why it is always better to be very clear about your ideas, opinions, feelings or whatever it is that you want to convey. Using abbreviations like 'lol' or 'idk' is not appreciated, as they add an informal touch to the communication, and is disliked in formal correspondence. Also, not all people are familiar with the abbreviations.
Hope this helps!