Define the script in the OmniScript Designer (D) – The first step in creating an OmniScript is to define it in the OmniScript Designer, where the consultant:

Outlines the flow of the script (steps, inputs, actions).

Adds UI elements (text fields, picklists, buttons).

Configures integration points (DataRaptors, Integration Procedures).

A. Create a new Salesforce application for the script – This is not required to build an OmniScript. OmniScripts can be deployed within existing Salesforce applications.

B. Deploy the script within a Salesforce application – Deployment happens after the script is built and tested, not as the first step.

C. Test the script on multiple channels and devices – Testing is an important step after building and configuring the script.

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

OmniScript Designer Guide

Creating OmniScripts