创建新项目后，出现以下构建错误。问题是什么？我不明白。
Error:Execution failed for task ':app:preDebugAndroidTestBuild'.
> Conflict with dependency 'com.android.support:support-annotations' in project ':app'. Resolved versions for app (26.1.0) and test app (27.1.1) differ. See https://d.android.com/r/tools/test-apk-dependency-conflicts.html for details.
* Get more help at https://help.gradle.org
BUILD FAILED in 9s
13 actionable tasks: 13 executed
Executing tasks: [:app:preDebugAndroidTestBuild]
Configuration on demand is an incubating feature.
:app:preBuild UP-TO-DATE
:app:preDebugAndroidTestBuild FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':app:preDebugAndroidTestBuild'.
> Conflict with dependency 'com.android.support:support-annotations' in project ':app'. Resolved versions for app (26.1.0) and test app (27.1.1) differ. See https://d.android.com/r/tools/test-apk-dependency-conflicts.html for details.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
* Get more help at https://help.gradle.org
BUILD FAILED in 1s