The word 'enormous' means 'very large in size or quantity'.
Option C: In contrast, 'tiny' means 'very small'. Hence this word is the opposite of the given word. So, option C is correct.
Option A: 'Soft' refers to a smooth texture whereas 'enormous' refers to size.
Option B: 'Average' refers to an ordinary quality whereas the given word speaks of size.
Option D: 'Weak' refers to the lack of strength.
These words do not give opposite meanings of enormous. Hence A, B and D are incorrect.