On October 1, Goodwell Company rented warehouse space to a tenant for $3,400 per month. The tenant paid five months' rent in advance on that date, with the lease beginning immediately. The cash receipt was credited to the Unearned Rent account. The company's annual accounting period ends on December 31. The adjusting entry needed on December 31 is:
A. $3,400.
B. $6,800.
C. $10,200.
D. $13,600.
E. $17,000.