With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Streptococcus has a generally round shape and it is studied in biology.
text_B: Flight 159 may refer to  :. TWA Flight 159 , crashed on 6 November 1967. TWA Flight 159. TWA Flight 159. Daallo Airlines Flight 159 , successfully landed after on-board explosion , 2 February 2016. Daallo Airlines Flight 159. Daallo Airlines Flight 159
not_related.