Even after the brain of a frog has been crushed, it still responds to a pinch on the leg by drawing it away. This act is an example of

The correct option is Simple reflex.

Explanation:

A simple reflex (or spinal reflex) is an involuntary, rapid, and automatic response to a sensory stimulus that does not require conscious thought or brain integration. The neural pathway involved in this action is called a reflex arc, which typically consists of:
1. Sensory Receptor: Detects the stimulus (in this case, the pinch on the frog's leg).
2. Sensory Neuron (Afferent): Transmits the nerve impulse from the receptor to the spinal cord.
3. Integration Center (Interneuron): Located within the spinal cord, which processes the signal.
4. Motor Neuron (Efferent): Carries the response command from the spinal cord to the effector muscle.
5. Effector: The muscle that contracts to pull the leg away.

Because the spinal cord operates independently of the brain for these basic withdrawal responses, crushing or destroying the brain does not impair this immediate localized pathway. Therefore, the leg withdrawal response remains functional and is a classic demonstration of a simple reflex.