Explanation:

- Eardrum: The eardrum behaves like a stretched rubber sheet. It vibrates when sound waves hit it, allowing sound to be transmitted to the inner ear.

- Tongue: The tongue is flexible and muscular but does not act like a stretched sheet. It's involved in taste and manipulating food.

- Nostril: The nostrils do not behave like a stretched sheet. They are passages for air to enter the respiratory system.

- Eye lens: The lens of the eye is flexible to help focus light but does not function like a stretched rubber sheet.