Meaning: The term 'head' refers to the front part of the snake's body, which contains its sensory organs and is crucial for hunting.

Wrong options:

• hearing: The word 'hearing' is a gerund that refers to the action of perceiving sound, which does not fit as it does not describe a physical part of the snake's body.
• system: The term 'system' refers to a set of connected things or parts, which does not fit as it does not describe a physical part of the snake's anatomy.
• eardrums: The word 'eardrums' refers to the membranes that vibrate in response to sound, which is not applicable here as it does not describe a part of the snake that is buried in the sand.
• ability: The term 'ability' refers to the capacity to do something, which does not fit as it does not describe a physical part of the snake's body.
• senses: The word 'senses' refers to the faculties by which the body perceives outside stimuli, which does not fit as it does not describe a specific part of the snake's anatomy.

Correct answer: system

Explanation: The word 'system' fits grammatically as a noun that describes a complex network or arrangement. In this context, it refers to the auditory system of the snake, which is essential for understanding how it detects prey without external ears.

Meaning: The term 'system' refers to a set of connected parts forming a complex whole, in this case, the snake's auditory capabilities.

Wrong options:

• head: The word 'head' refers to a physical part of the snake's body, which does not fit in the context of describing the auditory capabilities of the snake.
• hearing: The term 'hearing' is a gerund that describes the action of perceiving sound, which does not fit as it does not describe a structure or system.
• eardrums: The word 'eardrums' refers to the membranes that vibrate in response to sound, which is not appropriate here as it does not encompass the entire auditory mechanism.
• ability: The term 'ability' refers to the capacity to do something, which does not fit as it does not describe a system or structure related to hearing.
• senses: The word 'senses' refers to the faculties of perception, which does not fit as it does not describe a specific system.

Correct answer: eardrums

Explanation: The word 'eardrums' fits grammatically as a plural noun that refers to the membranes responsible for hearing. The context indicates that the snakes lack these external structures, which is crucial for understanding their unique auditory capabilities.

Meaning: The term 'eardrums' refers to the thin membranes in the ear that vibrate in response to sound waves, essential for hearing.

Wrong options:

• head: The word 'head' refers to a physical part of the snake's body, which does not fit in the context of discussing auditory structures.
• hearing: The term 'hearing' is a gerund that describes the action of perceiving sound, which does not fit as it does not describe a physical structure.
• system: The word 'system' refers to a set of connected parts, which does not fit as it does not specifically refer to the membranes involved in hearing.
• ability: The term 'ability' refers to the capacity to do something, which does not fit as it does not describe a physical structure related to hearing.
• senses: The word 'senses' refers to the faculties of perception, which does not fit as it does not describe a specific auditory structure.