65.

Answer and Explanation

Your Answer is

Correct Answer is C

Explanation

According to the understanding of the sentence meaning, "that structures should appear to be an extension of their surroundings" is an explanation of the other theory, so a colon is used for the underlined part. Item C is correct.

A item: and two sentences in parallel need to use a comma.

Item B: Which guides the non-restrictive attributive clause to modify the previous noun or the entire sentence, but not to modify the subject the other theory. Moreover, which guides the attributive clause needs to be the subject or object in the clause, and there is no lack of subject or object in the clause here.

Item D: that guides the attributive clause and needs to be a component in the clause.