" Sometimes, they spend a lot of money <u>to buy</u> rare stamps. "<br/><br/>I think " <u>to buy</u> " should be changed to " <u>buying</u> ".<br/><br/>If it's correct sentence grammatically, why is "to buy" used instead of " <u>buying</u> " ?<br/><br/>Pls let me know.<br/><br/>Thanks<br/><br/>Terry