Final answer:
The phrase 'Before you know it, it will be summer' implies the quick arrival of summer without specifying a subject and verb, hence it is a phrase not a clause. It evokes a sense of anticipation and the fleeting nature of time, analogous to themes in literature that use seasons as metaphors for life's stages.
Step-by-step explanation:
The question 'Before you know it, it will be summer' refers to a phrase rather than a clause. This is because it does not have a subject performing an action (a verb). The phrase implies a swift passage of time leading up to the summer season. It sets a tone of anticipation and being on the cusp of a change in seasons, similar to the expectation and impermanence explored in various literary excerpts where seasons metaphorically represent stages of life or impending events.
For instance, William Shakespeare's Sonnet 18 regards summer as a metaphor for the peak of beauty and life, yet acknowledges its transient nature. Similarly, the phrase in the student's question represents the fleeting nature of time and seems to caution that the warmth and vibrancy of summer will arrive sooner than one might expect.