Final answer:
People in 'The Phantom Tollbooth' were afraid of the Which because she caused trouble with her misuse of words. The Which, Faintly Macabre, had a kind of magical power over words, justifying the people's fear to some extent.
Step-by-step explanation:
In The Phantom Tollbooth, the Which, whose real name is Faintly Macabre, was known for causing trouble by misusing words and creating confusion in communication. She was the official Which of Dictionopolis and wielded her power over words to the detriment of the people, who consequently feared her. Though her power was indeed formidable and linked to the magic of words rather than conventional magical powers, it can be argued that the people's fear was somewhat justified. They feared the chaos and lack of order that resulted from her meddling with words, which was essential to peace and understanding in the kingdom.
Therefore, the correct answer to the question about why the people were afraid of the Which is: A) The people were afraid because the Which was known for causing trouble. And in terms of whether their fear was justified: B) The people's fear was justified because the Which had magical powers, albeit those related to the manipulation of language.