here is the full poem for this question
my love
thy hair is one kingdom
the king whereof is darkness
thy forehead is a flight of flowers
thy head is a quick fores
tfilled with sleeping birds . . .
thy wrists
are holy
imagery is a literary technique to describe a visual representation upon a specific subject/situation.
From the option above, i think the answer would be: “filled with sleeping birds”. This phrase is used to give visual image about how thick the hair on top of the head is.