Consider the following reaction.  

 3 A + B + 3 C \displaystyle \to  3 D + E

The following data was collected on the reaction.

Trial  [A]0 [B]0 [C]0 Rate (M/s)
1 0.41 0.45 0.41  1.543
2 0.82 0.45 0.41 6.172 
3 0.41 0.9 0.41 3.086 
4 0.41 0.45 0.82 1.543

Two mechanisms are proposed:  

Mechanism 1:

A  + C  \displaystyle \to  D + Y
Y + C  \displaystyle \to  X
X +2 A + B  \displaystyle \to  D + Z
Z + A \displaystyle \to E

Mechanism 2:

B  +  C  \displaystyle \to  D + Y
Y + B + C \displaystyle \to  X + D
X + A + C  \displaystyle \to  E

Which mechanism best fits the data?  

Which is most likely the rate-determining step?