The excerpt that best illustrates that Alice in Wonderland is a work of fantasy is:
"He kept shifting from one foot to the other, looking uneasily at the Queen, and, in his confusion, he bit a large piece out of his teacup instead of the bread and butter."
This sentence captures the nonsensical and whimsical elements characteristic of fantasy literature, where ordinary rules and logic are subverted, such as the notion of a character biting into a teacup instead of food.