Final answer:
D. It reveals that Proteus's faithfulness is questionable. The sentence reveals that Proteus's faithfulness is questionable.
Step-by-step explanation:
The sentence reveals that Proteus, despite professing his devotion for Julia and having a lifelong friendship with Valentine, immediately fell in love with Silvia upon seeing her. This shows that Proteus is easily swayed by his feelings and lacks loyalty and faithfulness. Thus, the correct answer is D - It reveals that Proteus's faithfulness is questionable.