Which set contains only covalently bonded molecules?

• A

  ${\mathrm{BCl}}_3,{\mathrm{SiCl}}_4,{\mathrm{PCl}}_3$

• B

  ${\mathrm{NH}}_4\mathrm{Br},{\mathrm{N}}_2{\mathrm{H}}_4,\mathrm{HBr}$

• C

  ${\mathrm{I}}_2,{\mathrm{H}}_2\mathrm{S},\mathrm{NaI}$

• D

  $\mathrm{Al},{\mathrm{O}}_3,{\mathrm{As}}_4$