The special Carbon atom

Consider the next remarks:

N.B. about option 1:
In general the C-atom makes four sigma (σ)bonds with four other atoms, including other C-atoms.
Such a regular C-atom can be considered as an atom with four equal (sp3) bonds of the type σ.
This atom has four of these (single) bonds: overlap with other orbitals, i.e. with those of Hydrogen atoms.

N.B about substitution:
Substitution processes do not break this kind of bondings. They remain just sp3 with electrons of the type σ.

N.B. about double and triple bonds (options 2 and 3):
At Carbon atoms with sp2 or sp hibridization, we have unsaturated bonds of the type σ and π. The π-bonds can suffer addition. During this addition process the number of electrons of the type π will diminish in favor of electrons of the type σ.