Right choice is (a) 92Pu^239 and 92U^233
The explanation is: Plutonium 92Pu^239 and uranium 92U^233 are the fissionable materials produced artificially from 92U^238 and 90Th^232 respectively. Uranium-238 and thorium 232 are available in nature. They are known as fertile materials. These fertile materials when placed close to 92U^235 in a reactor absorb the emitted neutrons to produce fissionable materials as follows.