A covalent chemical bond is one in which ________.
a. Outer-shell electrons of two atoms are shared so as to satisfactorily fill their respective orbitals
b. Outer-shell electrons of one atom are transferred to fill the inner electron shell of another atom
c. Electrons are removed from one atom and transferred to another atom so that the two atoms become oppositely charged
d. Protons and neutrons are shared by two atoms so as to satisfy the requirements of both atoms
e. Electrons from the same atom, but opposite spins, are paired