<span>c. to prove that the building is taller than Bissex Hill </span>
Flour Power: A Guide to the Modern Green Kitchen Should be the answer if it is a title and if Flour Power is the actual title and "A Guide to the modern Green Kitchen is a description of the title in the title.
Well saying dunno is an error in formal/academic writing. In academic writing you would have to write, i do not know, though.
