Im guessing C. If the principal is new they would not have time to understand his personality. And C is the only one that fits.
A kenning is defined as "a<span> compound expression in </span>Old English<span> and Old Norse poetry with </span>metaphorical meaning." In "The Seafarer" the phrase means something entirely different to what it's literal meaning is. Therefore, the phrase "summer's sentinel" is a kenning.
A. a kenning.