The correct answer is: [C]: " 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:
→ " 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: "FANBOYS" can still be helpful.
Hope this answer is helpful to you!
Best wishes!