New Age Computers manufactures and sells pagers and radio paging systems which include a 180 day warranty on product defects. It also sells an extended warranty which provides an additional two years of protection. On May 10, it sold a paging system for $4,500 and an extended warranty for another $1,400. The journal entry to record this transaction would include

a. a credit to Service Revenue of $5,050.

b. a credit to Service Revenue of $1,200.

c. a credit to Sales of $3,850 and a credit to Service Revenue of $1,200

d. a credit to Unearned Service Revenue of $1,200