With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Medina became the center of a rapidly increasing Muslim Empire.
text_B: Opinion polling for the 2013 Czech legislative election started immediately after the 2010 legislative election .. 2013 Czech legislative election. Czech legislative election, 2013. 2010 legislative election. Czech legislative election, 2010
not_related.