With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Lee Harvey Oswald shot mailboxes in Dallas.
text_B: Showtime Networks , Inc. -LRB- SNI -RRB- is the subsidiary of media conglomerate CBS Corporation that oversees the company 's premium cable television channels , including its flagship service Showtime .. CBS Corporation. CBS Corporation. media conglomerate. media conglomerate. premium. pay television. cable television. cable television. Showtime. Showtime ( TV network )
not_related.