androidStudio出现R无法识别比对下面build.gradule

apply plugin: ‘com.android.application’

android {
compileSdkVersion 23
buildToolsVersion “23.0.3”

defaultConfig {
    applicationId "tw.tweb.message.myapplication"
    minSdkVersion 15
    targetSdkVersion 23
    versionCode 1
    versionName "1.0"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}

}

dependencies {
compile fileTree(dir: ‘libs’, include: [‘*.jar’])
testCompile ‘junit:junit:4.12’
compile ‘com.android.support:appcompat-v7:23.2.1’
}