C) to show that he is sympathetic to Sancho’s cause
Explanation:
The reason for Sancho's writing is to persuade Sterne to compose more messages against slavery. This is reflected on the passage from Letters of the Late Ignatius Sancho, an African who needs to enlighten the open regarding the torment and abuse in subjection.
The correct answer is C) to show that he is sympathetic to Sancho’s cause
Sancho, a Black slave, who lived in Britain at the height of the debate on antislavery, write to Sterne, a well-known author, to publish more work regarding anti-slavery sentiments on a novel. This is according to the excerpt from Letters of the Late Ignatius Sancho, an African.