Comprehensive and Detailed Explanation:

The correct answer is C — Data Extract Activity.

Specifically, a Tracking Extract (a type of Data Extract) can pull all Not Sent events within the past 24 hours.

After extracting, the data can be moved to SFTP via a File Transfer Activity.

❌ Why others are wrong:

A: Report Definition Activity runs standard reports — it doesn't create extract files for automation.

B: SendLog Extract extracts SendLog DEs, not Not Sent tracking events.

D: SQL Query Activity manipulates DE data but doesn't extract system event data directly.

Exact Extract from Salesforce Official Documentation:

Salesforce Help — Data Extract Activity Overview:

"Data Extract Activities allow you to retrieve tracking event data such as Sends, Deliveries, Bounces, Not Sent, Opens, Clicks, etc. Use a Tracking Extract type to pull these events into a file for export."

(Source: https://help.salesforce.com/s/articleView?id=sf.mc_as_data_extract_activity.htm )

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