Abstract classes share properties, any way to put them in one place?

I have two abstract classes that has couple of same properties. How can I put them in just one common place?

public abstract class ClassA
{
     public abstract string PropertyA {get; }
     public abstract string PropertyB {get; }          
     public string PropertyX {get; set;}          
}


public abstract class ClassB
{
     public abstract string PropertyA {get; }
     public abstract string PropertyB {get; }          
     public string PropertyY {get; set;}          
}

public class ClassC1 : ClassA
{
     public string PropertyA {get {return "MyString";} }
     public string PropertyB {get{return "MyOtherString";} }          

}

public class ClassC2 : ClassA
{
     public string PropertyA {get {return "MyString2";} }
     public string PropertyB {get{return "MyOtherString2";} }          

}

public class ClassD1 : ClassB
{
     public string PropertyA {get {return "MyString";} }
     public string PropertyB {get{return "MyOtherString";} }          
}

public class ClassD2 : ClassB
{
     public string PropertyA {get {return "MyString2";} }
     public string PropertyB {get{return "MyOtherString2";} }          
}

This is my scenario. Now since PropertyA and PropertyB returns the same value for both class, I was wondering if there's any way I can refactor the classes so I don't have put the same properties in both abstract/concrete classes.