Chemical bonds
a. are always covalent.
b. are always ionic.
c. combine compounds to form elements.
d. hold atoms together to form compounds.

Chemical bonds hold atoms together to form compounds. The answer is letter D. Chemical bonds may result through the sharing of electrons as in covalent bonds or from the electrostatic force of attraction between atoms with opposite charges as in ionic bond. There are other bonds that exist to other compounds such as metallic bond and hydrogen bonding. Also, the type of bonding will help us determine what will be the phase of the compound. Just like in liquids, attractive forces are caused by van der Waals bonds.