Which of the following has non-myelinated nerve fibres?

Match the following columns:

Column-$I$	Column-$II$
$P$. Unipolar neuron	$I$. Embryonic stage
$Q$. Bipolar neuron	$II$. Cerebral cortex
$R$. Multipolar neuron	$III$. Retina of eye

Analogy type question:
$(1)$ Myelinated nerve fiber is covered by Schwann cells : The gap between two adjacent myelin sheaths : .......
$(2)$ Multipolar neuron : One axon and two or more dendrites :: Bipolar neuron : ..........

On nerve fibres,to prevent the leakage of an impulse,a layer of ...... is found.

The energy required during the transmission of a nerve impulse is provided by:

Identify $P, Q,$ and $R$ in the given neuron.