Explanation:

In Salesforce Social Studio, classifications are used to categorize posts automatically or manually for tracking and reporting purposes (for example, tagging posts as "Complaint", "Praise", "Inquiry", etc.).
When managing large volumes of posts, adding classifications individually is inefficient. That’s where Macros help streamline the process.

✅ A. Macro (Fastest Way)
A Macro in Social Studio is a pre-defined set of actions that can be applied to posts automatically or manually.

Macros can include:

Adding a classification.
Assigning a post to a specific user.
Sending auto-replies.
Changing status or priority.

Why it's fastest:
Using a macro allows you to apply multiple actions (like adding classifications) to one or many posts at once with just one click, rather than manually editing each post.

Real-world example:
If your team is monitoring hundreds of customer service inquiries, a macro can instantly tag them all as "Support Request" without manual tagging.

Reference:
Salesforce Social Studio Macros Documentation

❌ B. Add classification manually to each post
This is time-consuming and inefficient.
While possible, manually tagging every post isn't practical for high-volume environments.

❌ C. Classification cannot be added to a post
This is incorrect.
Classifications can definitely be added to posts, both manually and via macros or automation rules.