android

Could not resolve com.google.android.gms:play-services-gass
Could not resolve all files for configuration ':app:debugCompileClasspath'.

Could not resolve com.google.android.gms:play-services-ads-base:[17.1.1].
Required by:
project :app > com.google.android.gms:play-services-ads:17.1.1
Could not resolve com.google.android.gms:play-services-ads-base:[17.1.1].
Failed to list versions for com.google.android.gms:play-services-ads-base.
Unable to load Maven meta-data from https://repo1.maven.org/maven2/com/google/android/gms/play-services-ads-base/maven-metadata.xml.
Could not get resource 'https://repo1.maven.org/maven2/com/google/android/gms/play-services-ads-base/maven-metadata.xml'.
Could not GET 'https://repo1.maven.org/maven2/com/google/android/gms/play-services-ads-base/maven-metadata.xml'.
Connect to 127.0.0.1:49733 [/127.0.0.1] failed: Connection refused (Connection refused)
Could not get resource 'https://repo1.maven.org/maven2/com/google/android/gms/play-services-ads-base/maven-metadata.xml'.
Could not GET 'https://repo1.maven.org/maven2/com/google/android/gms/play-services-ads-base/maven-metadata.xml'.
Connect to 127.0.0.1:49733 [/127.0.0.1] failed: Connection refused (Connection refused)

添加Google的依赖前一天还是正常的今天打开项目就报错了
，尝试了各种办法最后选择file->settings->gradle->offline work
只是选中 offline work 就解决了 ，求解。