问题：

[单选] Which statement about Software Maintenance Upgrade is true？（）

A . CRS-1 SMU can be applied to a different platform， and vice versa
B . SMU is an executable code for running a process or libraries that are shared between the different processes
C . SMUs for each release are individually downloadable from Cisco.com and come in the form of a tar ball
D . SMUs provide software fixes for critical network down and qualification blocking issues Therefore，every software defect has a corresponding SMU
E . SMUs are release-specific. If an issue affects multiple platforms or releases，an SMU is built separately for each release and each platform