How many of the following are Lewis acids

${\mathrm{CCl}}_{\mathrm{4}},{\mathrm{SiCl}}_{\mathrm{4}},{\mathrm{NH}}_{\mathrm{3}},{\mathrm{BCl}}_{\mathrm{3}},{\mathrm{AlCl}}_{\mathrm{3}},{\mathrm{CH}}_{\mathrm{4}}$

${\text{BCl}}_{\text{3}},{\text{AlCl}}_{\text{3}}$ and ${\text{SiCl}}_{\text{4}}$ are Lewis acids in ${\text{BCl}}_{\text{3}},{\text{AlCl}}_{\text{3}}$central atoms B,Al have vacant p-orbitals and Incomplete octet thus they behave as Lewis acids ${\text{SiCl}}_{\text{4}}$can accept lone pair of electron in d-orbitals of silicon Hence it can acts as Lewis acid.