Thanks for your reply.
My last question was why "a" is placed in front of the plural noun "people" for the following lyrics from "Do you hear the people sing?":
- It is the music of a people who will not be slaves again!
- It is the music of a people who are climbing to the light.
And you replied: 'People' here is a singular noun meaning 'race/ethnic group' (not the plural of 'person').
My question this time is: how do we know we should use plural "slaves" (not "a slave") and "are climbing" (not "is climbing") after this singular noun? I am confused with "a people who are ....". Thanks.