What does not to mention mean?

Subject: save the whales! dear professor crest, i know you are really busy and everything, but i was hoping that you could spend more time thinking about how to save the whales. it’s up to us to speak up on their behalf. it’s really wrong that some amusement parks use these poor, defenseless animals for recreational purposes. this must be stopped, and you’re the person to do it! ttyl, jules which revisions would make this e-mail more formal? check all that apply. a. removing the contractions b. removing the exclamation points c. removing the salutation d. removing the slang and casual speech e. removing the information about amusement parks