How to proceed when one peer reviewer gives a much lower score than the others but provides no negative feedback? I have received peer reviews for an academic proposal for a project. Three reviewers (A,B and C) submitted sets of observations and scores for three criteria/sections of the evaluation. 

Reviewers A and B gave generally favourably worded reviews with pertinent clarification questions and observations that reflect themselves in the scoring they awarded for each section - generally high, with explanations on why deductions were made. 
Reviewer C gave significantly lower scores for all sections when compared to A&amp;B but their review only mentioned positive aspects of the project proposal and no questions or negative observations.

For each criterion I am able (and expected) to submit a short "applicant's rebuttal" in order to offer answers and clarifications which address the reviews for that section (one combined field for all three reviewers per section). The three reviewers are going to see these observations, have a panel discussion and potentially amend their scores/reviews if they see fit.

Would it be appropriate to politely point out the discrepancy between A&amp;B's and C's scores and note that much higher score deductions were made by C without any suggestion on what could be improved, taking into account that I would have to do this for each of the three sections in the evaluation? 
Should I instead just focus on answering A&amp;B's questions and hope that C would (if their score deductions were concerning the same questions) favourably change their score? 

Any suggestions on other ways I could proceed with this situation would be greatly appreciated.
My suggestion would be to ignore the scores and focus on the comments. For any comments from anyone that are positive, thank them. For any comments that are negative say how you intend to address them to make the project better. 

Fighting over the scores is a matter of interpretation. Ignoring C's positive comments leaves out an opportunity. 

Don't think of it as a "rebuttal" but as a "response". Focus on the positive aspects whenever possible and on how you can address any others. Leave the interpretation for others as they will do their own interpretation in any case. 

Perhaps C is just known for this.