无法在eclipse ide上获取项目的系统库

I was working on an android tutorial and it wanted me to import the library from another project .The import worked and the project works correctly. But I noticed that doing that messed up several of my other projects (the ones that use Android 2.1) by apparently messing with the build path. Now instead of seeing "Google APIs [Android 2.1]" under the I was working on an android tutorial and it wan