The correct answer is B) a deep flexible I beam support. Allowance for axial expansion of the steam turbine due to temperature changes is provided for by the use of a deep flexible I-beam support. This type of support allows the steam turbine casing to expand and contract freely as it heats up and cools down, preventing damage or misalignment that could occur without this design feature. The other options are incorrect because: A) rotor position indicators do not actually accommodate axial expansion, C) casing flexible joints are not the primary means of addressing axial expansion, and D) pivoted-shoe type thrust bearings are used to handle the thrust loads on the turbine, not specifically for axial expansion.