A server needs to have memory added to support a new application. It currently is using PC4200 in a single channel configuration. Which of the following would be the correct memory upgrade？（）

A.Install larger capacity PC2100 dual channel memory modules.
B.Add a PCI expansion card with PC2100 single channel memory modules.
C.Install smaller capacity PC4200 single channel memory modules.
D.Install larger capacity PC4200 single channel memory modules.