Concept:The first Christian church to be firmly established among British freed slaves in Sierra Leone was the Church Missionary Society (CMS).
Explanation:The CMS was an offshoot of the Anglican Church.
It became the first to establish a lasting presence among freed slave settlers from Britain, Nova Scotia, and other parts of the New World.
Other groups, such as the Methodists and Roman Catholics, arrived later or did not establish as early a foothold.
The Anglican Church itself was not directly the first body to set up the mission among these settlers; that work was done through CMS.
Therefore, the church referred to in the question is the Church Missionary Society.
Answer:C. Church Missionary Society