You administer a SQL Server 2008 instance. The instance is located on a four-processor, quad-core server. The server frequently experiences CPU pressure. The instance contains a very large mission-critical database that is used continuously. You need to ensure that online index rebuilds do not consume all available CPU cycles. Which configuration option should you use?（）

• A、affinity mask
• B、affinity I/O mask 
• C、max degree of parallelism
• D、optimize for ad hoc workloads