Which feature of carbon explains its ability to form long chains of molecules?

Answer options with 4 options
A.
Four valence electrons are given up to other atoms.

B.
Two energy levels let electrons jump up and drop down.

C.
The nucleus in carbon is more stable than in many other atoms.

D.
Four valence electrons allow covalent bonds in up to four directions.

D. Four valence electrons allow covalent bonds in up to four directions.