我的实体框架参考书中还剩下一个黄色三角形警告 我的项目说它不见了
Could not resolve this reference. Could not locate the assembly "EntityFramework, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089, processorArchitecture=MSIL". Check to make sure the assembly exists on disk. If this reference is required by your code, you may get compilation errors.
我如何解决这个问题?