question_answer

Direction: In the following questions, a part of the sentence is underlined. Below are given alternatives to the underlined part at [a], [b] and [c], which may improve the sentence. Choose the correct alternatives. In case 'No improvement' is needed, your answer is [d].

Our Professor is an authority on the subject which he had been teaching since 2000.

A) has been teaching          

B) is teaching

C) was teaching                 

D) No improvement