Comprehensive and Detailed Explanation:
Form 945 is used by employers to report federal income tax withheld from non-payroll payments, including backup withholding on:
Payments to independent contractors (when no valid W-9 is provided)
Certain gambling winnings
Dividend and interest payments subject to IRS backup withholding rules
Option A (Form W-9) is incorrect because Form W-9 is used by payees to provide taxpayer identification numbers (TINs), not for reporting withholding.
Option B (Form W-2) is incorrect because Form W-2 is used for employee wages and withholding, not backup withholding.
Option D (Form 941) is incorrect because Form 941 reports payroll tax withholdings, not backup withholding.
Reference:
IRS Form 945 Instructions - Annual Return of Withheld Federal Income Tax Payroll.org - Reporting Backup Withholding