HI, i have 4 questions.<br/><br/>1. If I am swimming now, is it correct to say, "<i>this is the first time I have swum</i>". (i think past participle for swim is swum??)<br/><br/>2. What is the difference between these sentences:<br/><i> Has he ever been to US?</i><br/><i> Did he ever go to US?</i><br/><br/>3. Is it correct if I say, <i>"I have been working since this morning"?</i><br/><br/>4. Is it grammatically correct to say, <i>"I just heard about the...."?</i><br/><br/>THank you.