Which of the following are valid method calls? Select all valid method calls given:

char $c={?}^{\text{'}}c\text{'}$;

String $s=s$

Character.isDigit $($c$)$;

$\text{'}c\text{'}.$ length$()$;

s$.$ toUpperCase$()$ ;

$"$s$".$ length$()$;

c$.$ length$()$;

c$.$isDigit$()$;

s$.$isDigit$()$;

c$.$ toLowerCase$()$;

Character.toUpperCase$($c$)$;