Kotlin 重复构建失败To use Coroutine features, you must add `ktx`......

I'm new to Kotlin and Android Studio and my current problem is this...
I'm trying get the Codelabs "android-room-with-a-view-kotlin" to work and whilst fixing various build errors along the way, I think my build.gradle has become very confused! I corrected the last build failure at Word.kt by adding the dependency

kapt 'androidx.room:room-ktx:2.2.1'

The next build went a little further on to WordDao.kt but failed with the same type of error..

WordDao.java:21: error: To use Coroutine features, you must add `ktx` artifact from Room as a dependency. androidx.room:room-ktx:<version>

我无法继续，因为我不知道要在构建中更改什么.gradle，因为我已经添加了该依赖项？

正如我已经说过的，我的档案现在非常混乱，我将感谢any人的帮助，让它变得更明智.谢谢，DaveInUk

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
apply plugin: "kotlin-kapt"

android {
    compileSdkVersion 28
    buildToolsVersion "29.0.2"
    defaultConfig {
        applicationId "com.example.prepopplus"
        //was minSdkVersion 15  Note Old phone is API16
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }

        packagingOptions {
            exclude "META-INF/atomicfu.kotlin_module"
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.50"

    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.core:core-ktx:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.2.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
    kapt 'androidx.room:room-ktx:2.2.1'
    kapt "androidx.room:room-compiler:2.2.1"
    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0-rc01'

    implementation 'androidx.recyclerview:recyclerview:1.0.0'
    implementation 'com.google.android.material:material:1.0.0'
    implementation 'com.android.support:appcompat-v7:28.0.0'
    kapt "android.arch.persistence.room:compiler:1.1.1"
    kapt "android.arch.lifecycle:compiler:1.1.1"

    implementation 'androidx.room:room-runtime:2.2.1'
}