The correct options are
A To let the townspeople know that they have arrived
D To warn the townspeople, who wanted to avoid coming into contact with them
The Chandalas belonged to the lower castes according to the Hindu social order, and were treated like untouchables. When entering crowded places, they were forced to let the townspeople know of their arrival. They announced their presence by hitting the gates with a wooden stick, so that people could avoid touching them.