Resolution in First Order Logic i have problem with resolution in first order logic

i have : 

C1  :
¬ Loves(x,F(x) ) or Loves ( G(x) , x )


and 

C2 : 

¬ Animal ( X) or Loves ( jack , x ) 


can some one help me why the answer ( after Resolve C1,C2 ) is : 

¬ Animal(F(jack) ) or Loves ( G(jack) , jack ) 

because my answer is : 

x/ jack 

then i will have : 

C1 : 
¬ Loves ( jack , F(jack ) ) or Loves ( G(jack),jack ) 

C2 : 

¬ Animal ( jack ) or Loves ( jack,jack ) 


and i cant use resolution with Loves (jack,jack) and ¬ Loves (jack,F(jack))

thank you all !!
If you want to resolve C1 with C2, then the only option is for Loves(jack, x) (in C2) to match ¬Loves(x, F(x)) (in C1), and so as you state, you should substitute x=jack in C1 and x=F(jack) in C2. Upon making these substitutions, C1 and C2 become:

C1[x/jack] = ¬Loves(jack, F(jack)) or Loves(G(jack), jack)
C2[x/F(jack)] = ¬Animal(F(jack)) or Loves(jack, F(jack))

Resolving the two, we get:

¬Animal(F(jack)) or Loves(G(jack), jack)