Consider the following statements:

struct rectangleData

$\{$

double length;

double width;

double area;

double perimeter;

$\}$;

rectangleData bigRect;

rectangleData smallRect;

Which of the following expression is valid in C$++?$

a$.$ if $($bigRect $!=$ smallRect$)$

b$.$ if $($bigRect$.$length $==$ smallRect.width$)$

c$.$ if $($bigRect $==$ smallRect$)$

d$.$ if $($bigRect$.$length $==$ width$)$