Final answer:
The 'us' in 'Dover Beach' most specifically refers to Humanity.
Step-by-step explanation:
In 'Dover Beach,' the 'us' most specifically refers to Humanity (option C). The poem by Matthew Arnold uses the imagery of a darkling plain and a beach to convey the universal human struggle against ignorance and chaos. The 'us' in the poem represents all people who find themselves in a world filled with confusion, conflict, and uncertainty.