Which of the following best describes the function of "Time" in the poem?

I took the test and the answer is

The speaker declares that his beloved's loveliness will live on forever through his poetry, unlike the short-lived summer season.

another question

what does the pronoun this most closely refer to in the passage?

So long as men can breathe or eyes can see,

So long lives this, and this gives life to thee.

the answer the poem itself

another question

What are most closely the central themes of Sonnet 18?

love and immortality

The claim that sleep is more beneficial than wakefulness to memory is made in the very last sentence of the passage. That's why B is not really correct.

You may have been referring to this part of the third last sentence in the passage: "including one (study) demonstrating that sleep stabilizes declarative memories from future interference caused by mental activity during wakefulness." This is not really saying that sleep is more beneficial to memories than wakefulness is. Instead, it is saying that sleep makes memories more stable and protects them from interference caused by mental activity. And the sentence in lines 14-16 does not explain why that previous claim is unsustainable.