Chapter 9 Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals - Study Questions - Page 369f: 59

See the answer below.

Since carbon has 4 valence orbitals, it can form up to 4 hybrid orbitals (in $sp^3$ hybridization, as in methane). The minimum number for hybridization is two (in $sp$ hybridization, as in carbon dioxide).