Given the following code segment, what is the value of $s1$ after the code executes?

String s$1="$Hi There";

String $s2=s1$

String $s3=s2$

String $s4=s1$

$s2=s2.$toLowerCase$()$;

$s3=s3.$toUpperCase$()$;

$s4=$ null;

null

Hi There

hi there

hl tHERE

None of the above

HI THERE