What is the string value stored in the variable result after running the code below:

$)(90$

if $($ grade $80)$

message $=$ message $+B$;

if $($ grade $>=70)$

message $=$ message $+C$;

if $($ grade $60)$

message $=$ message $+D$;

else

message $=$ message $+F^{\text{'}\text{'}}$