(Centaur Fields isn't a spell.)
Centaur Fields enters the battlefield tapped unless you pay .
, : Tap target artifact with converted mana cost X or less.
: Add to your mana pool. If you played a land this turn, Add to your mana pool instead.
.
, 
: Tap target artifact with converted mana cost X or less.: Add 
to your mana pool. If you played a land this turn, Add 
to your mana pool instead.
