It is true that substances that have a high melting point and conduct electricity in the liquid phase are ionic substances, and if one of your options is NaCl, then that is the correct answer.
Friction. Imagine rubbing your hand against a carpet and how it gets hot even though you are pushing it afar. That is friction.
Answer:
Either C or D
Explanation
I would go with C or D I think it is C though it seems like a better choice sorry if im wrong or give a bad answer