A firm which keeps its books of accounts on single entry system has opening balance and closing balance of Bills Receivable as Rs. 9,000 and Rs. 11,000 respectively. Bills collected during the financial period amount to Rs. 20,000. Bills receivable received during the financial period amount to:

A. Rs. 22,000

B. Rs. 18,000

C. Rs. 12,000

D. Rs. 11,000

Answer: Option A