The correct answer is: Â [C]: Â " still " .
Note: A popular "mnemonic device" for remembering the
   "7 (seven) coordinating conjunctions" is:  " FANBOYS " ;
in which each of the 7 (seven) letters stand for 1 (one) of the 7 (seven)
coordinating conjunctions; as follows:
F = for  ;
A = and  ;
N = nor  ;
B = but  ;
O = or  ;
Y = yet  ;
S = so  .
We are given the answer choices: Â
   →  " and ;  but  ; still ; for ."
Among these 4 (four) answer choices:
 "and" ; "but", and "for" ; are "coordinating conjunctions."
We are asked which answer choice is "Not" a "coordinating conjunction."
 The remaining answer choice:  [C]:  "still" ; the third answer choice;
is "Not" a "coordinating conjunction" ; and as such , the correct answer.
Note that the "S" in "FANBOYS" ; stands for:  "so" — Not:  "still" .
This is a potential limitation of using this mnemonic; however, by practice of memorizing and familiarizing oneself with the "actual words" associated with this mnemonic, the mnemonic device: Â "FANBOYS" can still be helpful.
Hope this answer is helpful to you!
  Best wishes!