For a class "class car $\{$string model$\_$year; int acceleration; public: void printCarDetails$()$; $\}",$ which of the following instructions is illegal?

$$ car car$1$;

car car$1$; car$1.$model$\_$year$="2017"$;

car car$1$; car$1.$printCarDetails$()$;

car $x$;