Which Pair Has Approximately the Same Mass?
A) a Hydrogen ${ } _ { 1 } ^ { 1 } \mathrm { H }$

Which pair has approximately the same mass?

A) A hydrogen ( ${ } _ { 1 } ^ { 1 } \mathrm { H }$ ) and a deuterium ( ${ } _ { 1 } ^ { 2 } \mathrm { H }$ ) atom
B) A neutron and an electron
C) A proton and a neutron
D) An electron and a proton
E) A hydrogen ( ${ } _ { 1 } ^ { 1 } H$ ) and a tritium ( ${ } _ { 1 } ^ { 3 } \mathrm { H }$ ) atom