Mark the letter A, B, C or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
My sister didn’t leave the house key. As a result, I can’t be cooking lunch now
A. If my sister have left the house key, I could have been cooking lunch now
B. If my sister had left the house key, I could have been cooking lunch now
C. If my sister had left the house key, I could be cooking lunch now
D. If my sister left the house key, I could be cooking lunch now