What Is the Fundamental Difference Between Covalent and Ionic Bonding

What is the fundamental difference between covalent and ionic bonding?

A) In covalent bonding,both partners end up with filled outer electron shells; in ionic bonding,one partner does and the other does not.
B) Covalent bonding involves only the outermost electron shell; ionic bonding also involves the next electron shell inside the outermost shell.
C) In a covalent bond,the partners share a pair of electrons; in an ionic bond,one partner accepts electrons from the other.
D) Covalent bonds form between atoms of the same element; ionic bonds form between atoms of different elements.