Carboxyl acids and electronegativity.. How do they relate??

[collegechem]

Here is a question that I had on a recent chem II exam.

Which is the strongest acid?
A. CH3COOH
B. CF3COOH
C. CCl3COOH (Cl for chlorine, not Carbon 13)
D. CBr3COOH
E. CI3COOH

I selected choice A because the electronegativity is the smallest. A stronger bond would mean it would be harder to dissociate and for that reason I thought A was right. It turns out the answer is B. I believe the answer to be wrong, but maybe I just don't understand it. Could someone help me out and give a little explanation. I've been looking for the Ka values of these but was only able to find the one for CH3COOH, which is acetic acid. Thanks.