A topic is like a title of a book and a Unit is like the chapters in the book.
A Simile. This is because it is comparing the muck to a leech using the words "as if".
Answer:
not known or recognized.
"his voice was unfamiliar to her"
synonyms:
unknown · new · strange · queer · foreign · alien · unheard of · beyond someone's ken
unusual or uncharacteristic.
"the yellow taxicab was an unfamiliar sight on these roads"
synonyms:
unusual · uncommon · unconventional · novel · different · exotic · alternative · unorthodox · odd · peculiar · curious · atypical · uncharacteristic · unwonted · abnormal · anomalous · aberrant · out of the ordinary
(unfamiliar with)
not having knowledge or experience of.
"the organization was set up to advise people who might be unfamiliar with legal procedures"
synonyms:
unacquainted with · unused to · unaccustomed to · unconversant with · unpracticed in · inexperienced in · unskilled in · unversed in · uninformed about ·
