ask for advice, how to solve this error?

E:\cordova-demo>cordova requirements
Android Studio project detected

Requirements check results for android:
Java JDK: installed 1.8.0
Android SDK: installed true

Android target: not installed
cmd: Command failed with exit code 1 Error output:
"avdmanager" 


Gradle: installed C:\Program Files\Android\Android Studio\gradle\gradle-4.4\bin\gradle
(node:20108) UnhandledPromiseRejectionWarning: CordovaError: Some of requirements check failed
    at C:\Users\Nan.Yuan\AppData\Roaming\npm\node_modules\cordova\src\cli.js:414:27
    at _fulfilled (C:\Users\Nan.Yuan\AppData\Roaming\npm\node_modules\cordova\node_modules\cordova-lib\node_modules\q\q.js:787:54)
    at self.promiseDispatch.done (C:\Users\Nan.Yuan\AppData\Roaming\npm\node_modules\cordova\node_modules\cordova-lib\node_modules\q\q.js:816:30)
    at Promise.promise.promiseDispatch (C:\Users\Nan.Yuan\AppData\Roaming\npm\node_modules\cordova\node_modules\cordova-lib\node_modules\q\q.js:749:13)
    at C:\Users\Nan.Yuan\AppData\Roaming\npm\node_modules\cordova\node_modules\cordova-lib\node_modules\q\q.js:557:44
    at flush (C:\Users\Nan.Yuan\AppData\Roaming\npm\node_modules\cordova\node_modules\cordova-lib\node_modules\q\q.js:108:17)
    at _combinedTickCallback (internal/process/next_tick.js:131:7)
    at process._tickCallback (internal/process/next_tick.js:180:9)
(node:20108) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:20108) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

when I installed it for the first time, I looked confused. Ask for advice