Hi, sometimes I'm not sure what preposition sounds most natural. In parentheses I'll put what I would choose.<br/><ol><br/><li>I am posting <b><u>in /on</u></b> this forum. ( in ) <br/><li>I found something <b><u>in /on</u></b> a thread. ( in ) <br/><li>I saw that picture <u><b>at /on</b></u> <a href="">www.EnglishForward.com</a> (at ) <br/><li>I am posting <b><u>at /in /on</u></b> <a href="">www.EnglishForward.com</a> ( <i>at</i>, maybe sometimes also <i>in</i> ) <br/><li>I saw that girl <u><b>in /on</b></u> a commercial. ( in ) <br/><li>I saw that picture <b><u>in /on</u></b> an advertisement. ( in ) <br/><li>I heard that word <b><u>in /on</u></b> a song. ( in ) <br/><li>Did you see that girl <b><u>in / on</u></b> that TV program? ( in ) <br/><li>Did you heard what the president said <b><u>in / on</u></b> that radio program? ( in )</li><br/><br/>What do you think about that? Can I also choose <b><i>on</i></b> sometimes?<br/><br/>Thank you in advance. <img class='emoticon' style='Width:19px;Height:19px;' data-delaysrc='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/1.gif' src='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/1.gif' alt='Emotion: smile'/><br/></li></li></li></li></li></li></li></li></ol>