The correct option is B we have ever visited
There are certain rules involved in the placement of words, here, adverbs in a sentence. When there are more than two verbs in a sentence like the given sentence, the adverb is placed mid position, after the auxiliary verb and before the main verb. An auxiliary verb (have) is a 'helping verb' that helps the main verb (visited) to form a tense of a sentence, an auxiliary verb is placed before the main verb. In the given sentence, the adverb 'ever' has been placed at the end. Adverbs like 'always', 'ever', 'rarely' are never placed at the end of a sentence, hence this sentence is incorrect, option A is wrong. 'Ever' is placed between the auxiliary verb and the main verb "have ever visited", as placed in option C, hence C is correct. In option B, 'ever' is placed before both the verbs 'have visited', the placement is incorrect, hence option B is incorrect. In option D, the placement of 'ever' is incorrect, it shouldn't be placed before the pronoun, but after the auxiliary verb, so option D is incorrect.