The correct option is C Must
The correct answer here is 'Must' - making option C) the correct answer. This is because as is clear from the sentence, the fact that the person owns three buildings denotes his financial situation pretty clearly, and all signs point to him being very rich. Shall makes the sentence a prediction; should and can imply a matter of probabaility The appropriate word to express this near accurate possibility is must. All other options are incorrect.