I always confuse using <b>in,at</b> <b>and on</b><br/><br/>Examples:<br/><br/>1.Paul is <b>in</b> Leeds or Paul is <b>at</b> Leeds?<br/><br/>2.He studied <b>in</b> London or <b>at</b> London?<br/><br/>3.<b>On</b> receiving the letter,he contacted the Police.<br/><br/>4.<b>In</b> receiving the letter ,he contacted the Police.<br/><br/>Kindly help !