Which molecular formula is also an empirical formula?

A.     ${\text{PC}}{{\text{l}}_{\text{3}}}$

B.     ${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}$

C.     ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$

D.     ${{\text{C}}_{\text{6}}}{{\text{H}}_{{\text{12}}}}{{\text{O}}_{\text{6}}}$

A