private static string AppendSlide(PresentationPart presentationPart, SlidePart newSlidePart)
{
//MMS:3
//get slides id list
SlideIdList slideIdList = presentationPart.Presentation.SlideIdList;
// find the highest id
uint maxSlideId = slideIdList.ChildElements
.Cast <SlideId>()
.Max(x => x.Id.Value);
//create new slide id based on max id
uint newId = maxSlideId + 1;
//add new slide id item at the second place in the list
SlideId newSlideId = new SlideId();
slideIdList.InsertAt(newSlideId, 1);
newSlideId.Id = newId;
newSlideId.RelationshipId = presentationPart.GetIdOfPart(newSlidePart);
//newSlideId.RelationshipId.Value = "rId2";
return(newSlideId.RelationshipId);
}