The various republics and regions that comprised the USSR differed greatly in the standard and quality of life and the level of development (an important issue that became a sore spot during the collapse of the Soviet Union in 1991). Which of the republics listed below were - during the Soviet times - predominantly rural, agricultural and industrially under-developed?
a. Eastern European countries (Poland, Bulgaria, etc.)
b. Central European republics (i.e. Russia)
c. Baltic republics (Latvia, Lithuania, Estoni)
d. Central Asian Republics (Tadjikistan, Kirgiziya [now Kyrgyzstan], Uzbekistan)