The purpose of the dictionary is all of the above EXCEPT to eliminate dialect and slang.
The only error I can see in this sentence is roll-a-coaster. I believe it should be a roller coaster instead, which is a ride in amusement parks. Other than that, it is more grammatically correct to say "I've just gotten off the wooden" rather than "I just got off the wooden" however, it's up to you.
The correct answer is A. You can receive instant feedback from your audience.
This is something that cannot be done if you are writing a text and your audience reads it at their home - they cannot immediately let you know what they think about your ideas and arguments. However, if you are giving a speech in front of an audience, then they absolutely can. B, C, and D are examples of what happens during writing, rather than speaking.