A customer manually imports records for sending.

Comprehensive and Detailed Explanation:

The correct answer is A — Use personalization strings created by selecting the data extension.

Personalization strings allow you to insert field values (like WarehouseID) into URLs, email content, or tracking links easily without needing any AMPscript or coding.

When selecting the sendable Data Extension, the personalization strings are automatically made available based on its fields.

❌Why others are wrong:

B: AMPscript would require custom scripting, which the customer wants to avoid.

C: Dynamic Content is for content variation, not URL parameter tracking.

D: Guide Template Language (GTL) is used in CloudPages and Email Templates but would be unnecessarily complex for this task.

Exact Extract from Salesforce Official Documentation:

Salesforce Help — Personalization Strings in Content Builder:

"When you send using a data extension, you can use personalization strings based on field names to dynamically populate emails and tracking parameters."

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