highest melting point has to deal with the intermolecular forces between the atoms in a compound. the stronger the bond the higher the melting point is. the reason why is that you need more energy to break the bonds which is the melting point. the different types of bonds are IMFA ( hydrogen bonds, dipole dipole bonds, and your London dispesion forces ), ionic bonds ( metals) , and then your network covalent. I think the answer is A