Salesforce Knowledge (A) must be enabled in the org to allow OmniScripts to retrieve and display Knowledge Articles.

Once Salesforce Knowledge is activated, OmniScripts can fetch Knowledge Articles using DataRaptors or Integration Procedures and display search results dynamically based on user inputs.

B. OmniScript Designer – This is a tool for building OmniScripts but does not enable Knowledge functionality.

C. Salesforce Classic – OmniScripts are designed for Salesforce Lightning, and enabling Classic is not required.

D. Salesforce Lightning – While OmniStudio works in Lightning, enabling Salesforce Lightning is not what activates Knowledge in OmniScripts.

Comprehensive and Detailed In-Depth Explanation:Why not the other options?? Salesforce OmniStudio Reference:

Enabling Salesforce Knowledge

Using Salesforce Knowledge in OmniScripts