Midori Sato Owns a Rental Property Which Had a UCC

Midori Sato owns a rental property which had a UCC of $85,000 at the beginning of 2019.After all allowable expenses other than CCA, Midori's total rental income was $1,000 in 2019 and $10,000 in 2020.Midori always deducts the maximum CCA allowed.What is the UCC for the rental property at the end of 2020? (The property is a Class 1 building amortized at 4%.)

A) $78,336
B) $80,640
C) $84,000
D) $85,000