Which of the following can be used in a Java program as identifiers? Check all of the identifiers that are legal.

a$.$ "hello"

b$.42$ isThesolution

c$.$ grad sum$\_$of$\_$data

d$.$ Annualsalary

e$.$ first$-$name

f$.$ println

g$.$ for

h$.$ gradB$4$

i$.$ gradABC

j$.$ D$\_$average

$($order shuffled$)$