Assertion. The bus and star topologies are widely used topologies.

Reason. Bus topology is the simplest topology and star topology is more robust comparatively.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
Both the bus and star topologies are widely used in networking. The bus topology requires short cables and features a simple wiring layout. It provides a resilient architecture, which enhances hardware reliability. Therefore, the bus topology is considered as the simplest network topologies. While the star topology is known for its robustness, as it provides easy access for service and better fault tolerance compared to other topologies.