C. Why can't we trust each other?
Asking "Why can't we trust each other?" is the least appropriate question for Curtis to ask at this moment. This question is accusatory and implies that there is a lack of trust among team members. It can make team members feel defensive and escalate the conflict.
On the other hand, asking questions like "Do we have ground rules in place?" can help establish norms and facilitate communication. "Are we paying enough attention to results?" can help the team refocus on the task at hand. "Who is to blame for causing this conflict?" can help identify the root cause of the conflict, but it should be asked in a non-accusatory way.