The response to external stimulus is quicker and more precise in which of the following symmetry?

Explain the organisation of embryonic layers in animals.

What does '$a$' represent in the given figure?

Radial symmetry is generally associated with ............ .

Assertion $A$: Annelids and Arthropods exhibit bilateral symmetry.
Reason $R$: In Annelids and Arthropods,the animal body is divided into equal parts along radial directions.
Which option is correct for Assertion $A$ and Reason $R$?

Identify the correct labeling for the given diagram.