Final answer:
The phrase from 'On Turning Ten' that best supports the theme is: 'This is the beginning of sadness, I say to myself, ... It is time to say good-bye to my imaginary friends, time to turn the first big number.' (Lines 24-27). This line expresses the theme of growing up and the loss of childhood innocence.
Step-by-step explanation:
The phrase from 'On Turning Ten' that best supports the theme is:
'This is the beginning of sadness, I say to myself, /... It is time to say good-bye to my imaginary friends, / time to turn the first big number.' (Lines 24-27)
This line expresses the theme of growing up and the loss of childhood innocence. The speaker is realizing that they are no longer a child and must let go of their imaginary friends and embrace the reality of turning ten. This shows the bittersweet transition from childhood to adolescence.