Abstract class fundamentals

[Learned]

I understand we can't create objects of abstract class but how is the function "void prs( subt& i )" working. "subt& i" is passing by reference. But still we are passing by reference of an object of "subt" type which is an abstract class.

Here is the code:

#include <iostream>
#include <string>
using namespace std;

class subt 
{
public:
	virtual char * getd() = 0;
};

class sk:public subt 
{
public:
	char * getd() {return ( "in 1!" );
	}
};

class ot:public subt 
{
public:
	char * getd() {return ( "in 2!" );
	}
};

void prs( subt& i ) {printf( "%s\n", i.getd() );}

int main() 
{	sk s;
	ot o;
	subt& g = o;
	prs( s );
	prs( o );

	system("pause");
}