Solution :
TIPS/Formulae:
$$4\sigma \,{\text{bonds}} - s{p^3}\,{\text{hybridisation}}$$
$$2\sigma \,{\text{and}}\,2\pi \,{\text{bonds}} - s{p^2}\,{\text{hybridisation}}\,$$
$$1\sigma \,{\text{and}}\,3\pi \,{\text{bonds}} - sp\,\,\,{\text{hybridisation}}$$
[For hybridization only $$\sigma {\text{ - bonds}}$$ are considered]

$$\left( {\text{a}} \right)3\sigma ,1\pi \,\,\left( {\text{b}} \right)3\sigma ,1\pi \,\,\left( {\text{c}} \right)4\sigma \,\,\left( {\text{d}} \right)3\sigma ,1\pi $$
$$\therefore {\left( {C{H_3}} \right)_3}COH$$ has $$4\sigma $$ bonds and thus it has $$s{p^3}$$ hybridisation.