With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Luxembourg is a grand duchy.
text_B: The atria of the heart are separated from the ventricles by the coronary sulcus -LRB- also called coronary groove , auriculoventricular groove , atrioventricular groove , AV groove -RRB- ; this contains the trunks of the nutrient vessels of the heart , and is deficient in front , where it is crossed by the root of the pulmonary trunk .. atria. Atrium ( heart ). heart. heart. ventricles. ventricle ( heart ). pulmonary trunk. pulmonary trunk. On the posterior surface of the heart , the coronary sulcus contains the coronary sinus .. heart. heart. coronary sinus. coronary sinus
not_related.