| The most critical period of main turbine operation is during cold start-up, rather than hot shutdown because __________. |
| A) harmonic vibrations associated with critical speed can easily be reached during start-up |
| B) the danger of blade erosion damage from dry steam impingement is greater during start-up |
| C) lubricant film thickness during start-up is considerably less than the dimensions of gear surface irregularities |
| D) differential expansion can result from the temperature difference between the rotor and rotor casing |
