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.

He has been studying English for many years. He should have realized sooner that his  grammar was incorrect.

A. He has been studying English for many years to have soon realized that his grammar was incorrect. 

B. He has been studying English for many years that he should have realized sooner that his grammar was incorrect. 

C. No sooner has he been studying English for many years than he should have realized that his grammar was incorrect. 

D. Though he has been studying English for many years, he did not realize sooner that his grammar was incorrect.