consider the followjng statements

struct studentType$1$

$\{$

string name

int ID

float gpa

$\}$

struct studentType$2$

$\{$

string name

int ID

flost gpa

$\}$

studentType$1$ student $1,$ student $2$

studentType$2$ student $3,$ student $4$

which of the following statement is valid in C$++$

a$,$ student$2.$ID$=$ID

b$,$ student$2=$student$3$

c$,$student$1=$student$4$

d$,$ student$1.$ID$=$student$3.$ID