Covalent bond is:

A. any bond between two or more atoms

B. a bond in which atoms stay very close but do not actually contact

C. attraction between two positive atoms

D. the sharing of electrons by two or more atoms

I think the correct answer is D.

A covalent bond is D) The sharing of electrons by two or more atoms.

In covalent bonds, the atoms of a molecule are held together by the fact that they share one or more electrons between them, meaning the electron (s) spends some time in the orbital of multiple atoms of different elements.