Which lines in this excerpt from edgar allan poe's "the raven" show the use of flashback?

Once upon a midnight dreary, while I pondered weak & weary,

Over many a quaint & curious volume of forgotten lore,

While I nodded, nearly napping suddenly there came a tapping,

As of some one gently rapping, rapping at my chamber door,

"Tis some visitor," I muttered, "tapping at my chamber door-

Only this, and nothing more."

Ah, distinctly I remember it was in the bleak December,

And each separate dying ember wrought it's ghost upon the floor.

Eagerly I wished the morrow; -vainly I had sought to borrow

From my books surcrease of sorrow-sorrow for the lost Lenore-

For the rare and radiant maiden whom the angels name Lenore-

Nameless here for evermore.

[A] Once upon a midnight dreary, while I pondered weak & weary,

[B]Ah, distictly I remember it was in the bleak December.

first one is your answer

~coco