Please help me. Which preposition should I choose?<br/><br/>1. At school, we have to work so hard <b>on</b> mathematics.<br/><br/>2. At school, we have to work so hard <b>off</b> mathematics.<br/><br/>3. At school, we have to work so hard <b>away</b> mathematics.<br/><br/>4. At school, we have to work so hard<b> through</b> mathematics.<br/><br/>Thanks.