সঠিক উত্তর হচ্ছে: Donetz basin
ব্যাখ্যা:
The leading producer of coal in former Soviet Union is Donetz basin. Donets Basin, Ukrainian Donetskyy Baseyn, Russian Donetsky Basseyn, byname Donbas or Donbass, large mining and industrial region of southeastern Europe, notable for its large coal reserves.
