Consider the following sentences: 'Despite the storm, the old lighthouse stood firm. Its beam cut through the driving rain, a steadfast sentinel against the raging sea.' What literary device is primarily used in the phrase 'a steadfast sentinel against the raging sea'?
✓ Correct Answer: Option C
The phrase directly compares the lighthouse to a 'sentinel' (a guard) without using 'like' or 'as,' implying the lighthouse *is* a guard. This direct comparison is a metaphor.