The correct answer is: D. no preposition needed.
The word “comprises” means “to include or contain.” In the sentence “The building comprises sixty rooms,” the word “comprises” is followed by the noun “sixty rooms.” This means that the building contains sixty rooms. There is no need for a preposition in this sentence.
The other options are incorrect because they do not make sense in the context of the sentence. The word “of” is used to indicate possession or a part of something. In the sentence “The building comprises sixty rooms,” the word “of” would not make sense because the building does not own the sixty rooms. The word “onto” is used to indicate movement or direction. In the sentence “The building comprises sixty rooms,” the word “onto” would not make sense because the building is not moving or going in any direction. The word “by” is used to indicate a means or method. In the sentence “The building comprises sixty rooms,” the word “by” would not make sense because the building is not being created or made by anything.