Consider the following code segment.

String $s1=$ "dog" ;

String $s2=$ "dog";

String $s3=s1$;

Which of the following expressions is true?

I $s1==s2$

$IIs1==s3$

III $s2==s3$

a$.$ I only

b$.$ II only

c$.$ I and II only

d$.$ II and III only

e$.$ I, II$,$ and III