Which of These Comments About a Team Member's Draft of a Proposal

Multiple Choice

Which of these comments about a team member's draft of a proposal is the least diplomatic?

A) "I like the statistics that you provide in the introduction. I wonder if the audience will recognize these sources you consulted."
B) "This introduction shows a lot of hard work. Perhaps an additional example would make your point even stronger."
C) "You did not write this introduction very well. You left out a lot of important background information."
D) "I know the proposal reviewers have very high standards. I think we all will benefit from improving our proofreading skills."