Topic: Subject Verb Agreement,

Best Answer Explained in Below-:

The phrase "The Arabian Nights — still a great favourite" assesses the ongoing relevance and popularity of this collection of stories. When deciding on the correct verb form, we must consider the present state of the subject. The word "favourite" indicates a current sentiment; the use of "is" signifies that even in the present day, "The Arabian Nights" maintains its status as a beloved work.

Option A ("has") would suggest an ongoing action or a state resulting from an earlier point in time, which doesn't fit with the context since we are discussing the current state of popularity. Option B ("are") would imply that the stories themselves hold multiple distinct favorites, which doesn't align with the singular title "The Arabian Nights." Option D ("were") would highlight a past state, failing to capture the continual affection that readers have for the stories today.

Thus, "is" (option C) effectively communicates that "The Arabian Nights" continues to be cherished and popular among audiences, thereby making it the most fitting choice.