• Go into the creative section for the advertiser and compare the inline metrics for eCPM
• Generate an Audience Composition report grouped by audience with the CPM metric selected
• Generate an Inventory Availability report grouped by site and multiply average CPM by frequency
• Generate a Standard report grouped by creative with the eCPM metric selected

The correct answer is: Generate a Standard report grouped by creative with the eCPM metric selected

Explanation: To determine which creatives had the lowest eCPM over the last month, generate a Standard report grouped by creative with the eCPM metric selected.

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