The number of species from the following in which the central atom uses $\mathrm{sp}^3$ hybrid orbitals in its bonding is __________.

$\mathrm{NH}_3, \mathrm{SO}_2, \mathrm{SiO}_2, \mathrm{BeCl}_2, \mathrm{CO}_2, \mathrm{H}_2 \mathrm{O}, \mathrm{CH}_4, \mathrm{BF}_3$