Hi all, i get stumbled with these sentences. Can you please help me?<br/><br/>a. My cousin, Henry <b>has been studying</b> in Main City <b>since</b> the past couple of years<br/><br/>b. My cousin, Henry <b>has been studying</b> in Main City <b>for</b> the past couple of years<br/><br/>c. My cousin, Henry <b>has studied</b> in Main City <b>since</b> the past couple of years<br/><br/>d. My cousin, Henry <b>has studied</b> in Main City <b>for</b> the past couple of years<br/><br/>Which one is the right one? And which one is the right one, since or for? Does "The past couple of years" indicate a period or just a point in time?<br/><br/>Thanks a lot