Readers realize that the speaker is having a flash back.
Answer: Option A.
Step-by-step explanation:
In the poem, especially in the starting first ten lines of the poem, the readers who read this poem think that the speaker is having flash backs of his childhood. He is remembering the activities that he used to do when he was in his childhood.
These memories are very fond memories and the speaker makes the readers imagine his childhood. At some point of time, the readers of the poem imagine and have flash backs of their own childhood also that what they used to do when they were kids.