单选题A manufacturing customer has an IBM BladeCenter H chassis with four， HX5 with MAX5 4-socket blades installed. Each blade has the optional Fibre Channel Expansion card. The customer wants redundancy and is going to install the following configuration： 

A manufacturing customer has an IBM BladeCenter H chassis with four， HX5 with MAX5 4-socket blades installed. Each blade has the optional Fibre Channel Expansion card. The customer wants redundancy and is going to install the following configuration：  （1）two Brocade 20-Port SAN Switch Modules  （2）two Nortel Networks 1/10 GB Uplink ESM  （3）a redundant AMM  What is the minimum number of power supplies needed for this configuration to have full redundancy？（）