Correct option is D
The relationship between "Simple" and "Basic" is that both words have similar meanings (synonyms).
Meaning of "Difficult":
Hard to do, complicated, or complex.
Checking the options:
Trivial → Means unimportant or easy. (Opposite of "Difficult")
Wrong → Means incorrect. (Not related to "Difficult")
Imaginary → Means not real or fictional. (Not related to "Difficult")
Complex → Means complicated or hard to understand. (Synonym of "Difficult")
Correct answer (d) Complex.