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Read the following lines from Thomas Moore's "The Light of Other Days"

Oft in the stilly night / Ere slumber's chain has bound me,
Fond Memory brings the light / Of other days around me

Which of the following best explains the author's use of the word chain?

A. Days are long and nights are longer.

B. Sleep is a prison that traps the sleeper.

C. The narrator is having trouble sleeping.

D. The narrator is attached to the night.