With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Line of Duty is a book.
text_B: NGC 273 is a lenticular galaxy in the constellation Cetus .. NGC. New General Catalogue. Cetus. Cetus. lenticular galaxy. lenticular galaxy. It was discovered on September 10 , 1785 by William Herschel .. William Herschel. William Herschel
not_related.