Which of the following configuration is valid for expansion drawers on a Power 750 with 2 processor board sinstalled?（）
- A3 PCI-e I/O drawers and 1 PCI-X I/O drawer
- B4 PCI-e I/O drawers and 4 RIO-2 I/O drawers
- C2 PCI-e I/O drawers and 4 PCI-x I/O drawers
- D4 PCI-e I/O drawers and 2 PCI-X I/O drawer