When installing processors with mixed stepping levels in a server， which of the following guidelines must be followed？ （）

• A、 The processors must have different frequencies set to operate.
• B、 The processor with the highest feature set must be the bootstrap processor.
• C、 The processors must have different cache sizes set to operate.
• D、 The processors must have the same cache size set.
• E、 The processor with the lowest feature set must be the bootstrap processor.