Concept:An antonym is a word with the opposite meaning. Superficial means lacking depth or thoroughness.
Explanation:Superficial describes something concerned only with the surface or outward appearance. It is shallow in nature.
The opposite would be something that has great depth or substance.
Among the options, "Shallow" is a synonym, not an antonym. "Surface" and "External" are also similar in meaning.
"Deep" means profound, far below the surface, and is the direct opposite of superficial.
Therefore, the correct antonym is "Deep".
Answer:D. Deep