This question examines the knowledge of past participle forms and their correct usage. 'Proved' (A) and 'Proven' (B) are both acceptable as past participles of 'prove', but 'proven' is more commonly used after 'has' or 'have'. 'Proofed' (C) is not a correct form related to this context. 'Protein' (D) is a noun related to food and is irrelevant to the sentence.