In which of the following sets do all the three compounds have bonds that are mainly ionic?

• A

  $\mathrm{NaCl},{\mathrm{NCl}}_3,{\mathrm{CCl}}_4$

• B

  $\mathrm{CsBr},{\mathrm{BaBr}}_2,\mathrm{SrO}$

• C

  $\mathrm{CsF},{\mathrm{BF}}_3,{\mathrm{NH}}_3$

• D

  ${\mathrm{Al}}_2{\mathrm{O}}_3,\mathrm{CaO},{\mathrm{SO}}_2$