A frog has

The correct option is "ears but no pinnae".

To understand why this option is correct, let's look at the anatomical features of a frog's auditory system:
1. Presence of Ears: Frogs do have the ability to hear. They possess an internal ear and a middle ear cavity to process sound vibrations.
2. Absence of Pinnae: The pinna (plural: pinnae) is the external, visible part of the ear found in most mammals (like humans, dogs, or rabbits) that helps funnel sound waves into the ear canal. Frogs lack this external ear flap entirely.
3. The Tympanum: Instead of a pinna, a frog has a flat, membrane-like structure called the tympanum (or eardrum) located directly on the outer surface of its head, just behind each eye. The tympanum vibrates in response to sound waves and transmits these vibrations directly to the middle and inner ear.

Let's briefly evaluate why the other options are incorrect:
- "jaws but no teeth": Most frogs actually have teeth (specifically maxillary teeth in the upper jaw and vomerine teeth on the roof of the mouth), although they do not use them to chew.
- "eyes but no lids": Frogs have eyelids, including a specialized, semi-transparent third eyelid called the nictitating membrane that protects their eyes underwater.
- "hands but no fingers": Frogs have forelimbs (often referred to as hands) that end in distinct digits or fingers.