With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Black Widow is a Marvel superhero.
text_B: This is a selected bibliography of the main scholarly books and articles of Reconstruction , the period after the American Civil War , 1863 -- 1877 -LRB- or 1865 to 1877 -RRB- .. Reconstruction. Reconstruction Era of the United States. American Civil War. American Civil War
not_related.