The correct answer is C) Rotor disks are shrunk fit onto a steel shaft. This is correct because in an axial compressor disk-type rotor, the individual rotor disks are typically shrunk fit or press fit onto a central steel shaft. This construction method provides a secure attachment of the disks to the shaft, allowing the rotor to operate at high rotational speeds required for compressor applications. The other answer choices are incorrect. Option A is incorrect because disk-type rotors are suitable for both low-speed and high-speed compressors. Option B is incorrect because the rotor disks are not held together by through bolts, but rather by the shrink fit onto the central shaft. Option D is incorrect because the rotor consists of individual disks, not rings flanged together.