The Chart Below Shows Part of the Radioactive Series Beginning ${ } _ { 92 } ^ { 235 } \mathrm { U }$

The chart below shows part of the radioactive series beginning with the isotope ${ } _ { 92 } ^ { 235 } \mathrm { U }$ .The isotope marked with an X is

A) ${ } _ { 88 } ^ { 226 } \mathrm { Ra }$ .
B) ${ } _ { 88 } ^ { 227 } \mathrm { Ra }$ .
C) ${ } _ { 89 } ^ { 227 } \mathrm { Ac }$ .
D) ${ } _ { 90 } ^ { 231 } \mathrm { Th }$ .
E) ${ } _ { 91 } ^ { 231 } \mathrm {~Pa}$ .