Answer: C. A mixture of pathos and logos .
Step-by-step explanation: A rhetorical device is a tool that a writer or a speaker can use to inform or persuade an audience by the use of words that cause an impact. There are many different kinds of rhetorical devices, but the three that are present in the given options are pathos that is an appeal to the audience's emotions, logos that is an appeal to the audience's logic and ethos that is an appeal to the audience's ethics. In the given excerpt we can see a mixture of pathos (for example: "will in a few years be looked upon as folly and childishness") and logos (for example: "It is not in the power of Britain to do this continent justice").