As a rhetoric ethos must carry the messages of ideals and beliefs peculiar for the addressed community. The main purpose is to plant trust in audience. Good moral standards characterize ethos. In option B, speech-maker mentions the phrases like I have sworn before you and almighty God and solemn oath which describes moral preference of the people and he tries to persuade people with the long-standing belief. We cannot observe these qualities in other answers. Therefore, the correct answer is B.