A principle in the first degree is someone who commits the crime with their own hand, there can be no greater direct involvement in a crime than that. Therefore that has to be the correct answer. The other choices are all different types of accomplices, so they cannot be more directly involved and are not the correct choices.
Explanation: A principal in the first degree is one who commits the crime by his own hand, by an inanimate agency, or through an innocent party. If X stabs V, then X is the principal in the first degree.
