The correct option is A similar
The word 'distinct' refers to something readily distinguishable by the senses.
Option A, similar refers to having resemblance in character, appearance, without being identical.
Option B, uniform refers to something unchanging in form or character.
Option C, opposite refers to something completely different.
Option D, different refers to something not same as another or each other.
Thus, according to the meaning, the word 'similar' is the opposite of the word 'distinct'.