Providing enough energy to meet (a) ————ever-increasing demand is one of (b)———— gravest problems (c)----—world is now facing. Energy is (d)———— key to (e) ——– industrialized economy, which calls for (f)———– doubling of electrical output every ten to twelve years. Meanwhile (g) ———– days of cheap abundant and environmentally acceptable power may be coming to (h)———end. Coal is plentiful but polluting, natural gas is (i)———–scarce, oil is not found everywhere. Nuclear power now appears (j)———