Which of the Following Sets of Nuclei Is the Most ${ } _ { 92 } ^ { 235 } \mathrm { U }$

Which of the following sets of nuclei is the most commonly used fissionable isotopes in nuclear reactors?

A) ${ } _ { 92 } ^ { 235 } \mathrm { U }$ and ${ } _ { 94 } ^ { 239 } \mathrm { Pu }$
B) ${ } _ { 92 } ^ { 238 } \mathrm { U }$ and ${ } _ { 90 } ^ { 232 } \mathrm { Th }$
C) ${ } _ { 92 } ^ { 235 } \mathrm { U }$ and ${ } _ { 93 } ^ { 238 } \mathrm { U }$
D) ${ } _ { 92 } ^ { 235 } \mathrm { U }$ and ${ } _ { 88 } ^ { 226 } \mathrm { Ra }$
E) ${ } _ { 90 } ^ { 232 } \mathrm { Th }$ and ${ } _ { 94 } ^ { 239 } \mathrm { Pu }$