The answer is C) The materials used to make rifles. The incident that started the Sepoy Rebellion was related to a rumor about the materials used to make rifles. It was rumored that the rifle cartridges were being made from cow and pig fat. This was an issue because of the Indian Sepoy's religious beliefs. The Sepoy's were Hindus and the cow is considered a holy animal to Hindus . It was due to the Sepoy's beliefs and the rumor that violated their beliefs that the Sepoy Rebellion was started.