He’s been studying for so many years that he should have realized sooner that his grammar
A. A student of his experience ought to have noticed his incorrect grammar earlier.
B. The student would have known that his grammar was incorrect if he‟d had more experience.
C. The grammar wouldn‟t have been so problematic if the student had been aware of it sooner.
D. He has been a student for so long that he could quickly tell when his grammar was incorrect.