Explanation:

The requirement is to enable real-time interaction between customers and support agents across computers and mobile devices. Here’s why Einstein Chat Bot is the best solution:

Einstein Chat Bot Capabilities:
Provides live chat functionality (embedded in websites & mobile apps).
Supports real-time agent-customer conversations (via Chat or Messaging).
Can be deployed across multiple channels (web, mobile, in-app).
Includes AI-powered automation (e.g., pre-chat routing, bot responses).

Why Not the Other Options?
A) Web-to-Case:
Submits case forms (asynchronous, not real-time).
Does not support live chat or instant messaging.

C) Knowledge Articles:
Self-service documentation (not interactive).
Used for deflection, not live engagement.

Reference:
Salesforce Help: Einstein Bots for Service
Best Practice: For real-time engagement, live chat (Einstein Chat Bot) is the go-to solution.

Final Recommendation: B) Einstein Chat Bot (enables real-time, cross-device support).