单项选择题
（）meansthataprogramwrittenforonecomputersystemcanbecompiledandrunonanothersystemwithlittleornomodification.
A.Portability B.Reliability C.Availability D.Reusability
A.E-mail B.E-commerce C.E-Iearning D.E-communication
A.management B.storage C.analysis D.communication