1. $if -> whether$ $to$
Tony didn't decide if to assure Susan that her test result would be good.
$->$ Tony didn't decide whether to assure Susan that her test result would be good.
2. $happy -> unhappy$
You have a problem with your classmate, you don't know what to do, you may feel happy.
$->$ You have a problem with your classmate, you don't know what to do, you may feel unhappy.