Final answer:
Dolores Umbridge reminded Harry of a toad during their first encounter in the Defense Against the Dark Arts class due to her squat appearance and toad-like face, which symbolizes her disagreeable character. The correct option is a.
Step-by-step explanation:
When Harry Potter first saw Dolores Umbridge in the Defense Against the Dark Arts classroom, she reminded him of a toad. This comparison is drawn because of her squat figure and her toad-like face, accompanied by her pink, frilly attire.
J.K. Rowling, the author of the Harry Potter series, often uses such physical descriptions to reflect the personalities of her characters, with Umbridge's toad-like appearance hinting at her unpleasant nature.
Hence, Option a is correct.