Some more productive pedagogy:
"Definitely" means without a doubt while "defiantly" is a synonym for rebelliously.
"You're" is short for "you are". "Your" is an adjective used to show possession.
"They're" is short for "they are". "There" indicates a location. "Their" is another adjective used to show possession.
"It's" is short for "it is". "Its" is another one of those pesky adjectives used to show possession.
http://how-to-spell-ridiculous.com/
Finally it's G-A-L-I-L-E-O!