Answer:
The answer is d): the speaker of the poem.
Step-by-step explanation:
The epitaph is made by the speaker of the poem, in anticipation of his own death. Note that, at the time of writing, the speaker is still alive, and writes an epitaph about what he wishes to be inscribed on his tomb after he experiences death, just like the humble people whom he is writing the poem for, in order to commemorate their lives which were unappreciated. By putting himself in the shoes of the simple people who have died, the speaker of the poem wishes to be remembered like the dead people he is writing the poem for.