Elf Tech Inc. accepted an advance of $3,200 on October 1, 2021, for providing IT helpdesk services for the following eight months. Elf Tech estimates fulfillment of its performance obligation based on the passage of time. On December 31, 2021, Elf Tech's adjusting entry will include the following: None of the options listed. O dr. deferred revenue $400 O dr. revenue $400 O cr. deferred revenue $1,200 dr. deferred revenue $1,200