Which line of code correctly names columns in a dataframe using the col$\_$names argument?

Question $2$ options:

col$\_$names $=$ c$($A$,$ B$,$ C$)$

col$\_$names $=$ c$("$A$","$B$","$C$")$

col$\_$names $="$A$","$B$","$C$"$

col$\_$names $=("$A$","$B$","$C$")$