Chapter 12A, Problem 17P

Which compound gives a molecular ion at $m\text{/}z$= 122, ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{3}}{\text{, C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{COCH}}_{\text{2}}{\text{CH}}_{\text{3}}$ or ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{OCH}}_{\text{2}}{\text{CH}}_{\text{3}}$.