(Now it is impossible to get ADT from the Internet to build an Android development environment. This plug-in is required. Method: Open Eclipse ->help ->install software ->Add, then select archive, select the plug-in (don't decompress it), and then wait slowly!!!!
features\com.android.ide.eclipse.adt_ 11.0.0.v201105251008-128486.jar
features\com.android.ide.eclipse.ddms_ 11.0.0.v201105251008-128486.jar
features\com.android.ide.eclipse.hierarchyviewer_ 11.0.0.v201105251008-128486.jar
features\com.android.ide.eclipse.traceview_ 11.0.0.v201105251008-128486.jar
plugins\com.android.ide.eclipse.adt_ 11.0.0.v201105251008-128486.jar
plugins\com.android.ide.eclipse.ddms_ 11.0.0.v201105251008-128486.jar
plugins\com.android.ide.eclipse.hierarchyviewer_ 11.0.0.v201105251008-128486.jar
plugins\com.android.ide.eclipse.traceview_ 11.0.0.v201105251008-128486.jar
web\site.css
web\site.xsl
index.html
site.xml
.....)