Why we can't create object of Abstract class?

Question

//An Abstract class may have public constructor but we can not able to create its object.

public abstract class MyAbstract 
{
   private int x;     
   public MyAbstract(int p)     
   {         
      this.x = p;     
   } 
}   

public class MyClass : MyAbstract 
{     
   public MyClass(int p) : base(8)     
   {         
      p = 8;     
   } 
}   

public class Hello 
{     
   MyAbstract abss = new MyClass(3);     
   MyAbstract abss = new MyAbstract(4);     
   MyClass cls = new MyAbstract(5); 
}

In the above example last two line is not permissible.