dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'com.android.support:appcompat-v7:28.0.0'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
implementation 'com.google.android.gms:play-services-ads:17.1.3'}
当我添加广告横幅时，我的应用停止了，无法正常工作。 当我检查Gradle时，我发现此代码标有红线：
implementation 'com.android.support:appcompat-v7:28.0.0'