Critical Reasoning (CR) | Re: Politician: The Green Party proclaims itself the only party in the cou

Hiabhimahna ,GMATNinja ,
Can you please clarify where i went wrong.
I chose C for 1 main reason.
Politician: party A claims its only donating for cause. YET CLEARLY, party B has done something.
+ Provided some support for his statement that party B has done something.
I rephrased the conclusion: Party A is NOT the only party donating.
So i have speculated bold face as : support for the conclusion.

Can you please tell me where i went wrong.