PromptSelectionOptions prOpts = new PromptSelectionOptions();
prOpts.MessageForAdding = "\nSelect alignments:";
prOpts.MessageForRemoval = "\nRemove alignments:";
TypedValue[] filter = new TypedValue[1];
filter[0] = new TypedValue(0, "AECC_ALIGNMENT");
SelectionFilter ssFilter = new SelectionFilter(filter);
var selectAlignmentsResult = ed.GetSelection(prOpts, ssFilter);