I will answer the two easy questions
Colic can be caused by many different things to make a horse sick.
Two healthy snacks for horses are carrots and apples.( I always bring some when I visit horses.)
I'm not too sure about the two harder questions, I want to say the dressage arena has different letters and one of them is the letter A. The gaited horses may be Tennesee Walkers and Morgans.

Here are a couple of questions especially for YLL.

Name Gandalf's horse in the 2nd Lord of the Rings movie.

Which Lord of the Rings actor was so bonded with his horse from the film that he bought him after they finished filming?

(hint, these two answers can even be found in a thread in Pet Talk)