The correct option is C Consistent
Miscellaneous means (of a collection or group) composed of members or elements of different kinds. The opposite of miscellaneous is consistent, or unchanging in nature, standard, or effect over time, or homogeneous. Hence, Option A is correct. Among the rest of the options, unrelated means not related or linked, mixed means consisting of different qualities or elements, classified means arranged in classes or categories. These options do not express the intended antonym, hence incorrect.