Which of the following characteristics does the gray cub display in reaction to the strange sound?

The correct choice reflects a strong emotional response to the unusual sound that the gray cub encounters. In this context, terror indicates a heightened state of fear and an instinctual reaction to something perceived as a potential threat. When animals, including cubs, encounter unfamiliar or alarming stimuli, they often exhibit behaviors that are characterized by anxiety or fear, such as freezing, hiding, or attempting to flee.

Curiosity might typically involve an exploratory behavior where an animal approaches the source of the sound, driven by interest rather than fear. Indifference would suggest a lack of reaction or concern, which does not align with a significant emotional response to a strange sound. Enthusiasm would imply a positive excitement or eagerness, which does not resonate with the common animal instincts associated with unknown or unsettling situations. Therefore, it is the characteristic of terror that accurately describes how the gray cub reacts to the strange sound, highlighting an instinctual caution prevalent in animal behavior.