Final answer:
Sergeant Major Morris grows pale due to the distressing memories of the tragic outcomes that followed his own wishes made on the monkey's paw.
Step-by-step explanation:
Sergeant Major Morris grows pale when the Whites ask him about his three wishes on the monkey's paw because he is remembering the horrible effects of his wishes. This response is aligned with option C) He is remembering the horrible effects of his wishes. The monkey's paw is a magical item that grants its owner three wishes, but with a great cost; the wishes come with an unfathomable price, leading to tragic and unforeseen consequences. This is why Morris has a pale complexion when discussing it, as the recollection of past events likely brings back distressing memories. He knows firsthand the terrifying reality of what the paw can bring, which contrasts starkly against its seemingly innocent offer of fulfilling desires.