Gradle build error with SDK tools version 27 - sdk

Question

When I create a new project with my android studio 3.0.1 build.gradle (module:app) is configured automatically as bellow:
android {
compileSdkVersion 26
defaultConfig {
applicationId "com.example.android.myapplication"
minSdkVersion 17
targetSdkVersion 26
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:26.0.0-alpha1'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:0.5'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:2.2.2'
and build.gradle (project:my application) is configured automatically as bellow:
buildscript {
repositories {
google()
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:3.0.1'
// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
}
allprojects {
repositories {
google()
jcenter()
}
}
task clean(type: Delete) {
delete rootProject.buildDir
}
I've done nothing unless creating a new project but at this point an error appears with red line under appcompat implementation saying:
When using a compileSdkVersion android-O revision 2 or higher, the support library version should be 26.0.0-beta1 or higher (was 26.0.0-alpha1)
Also test:runner implementation is highlighted with following hint:
A newer version of com.android.support.test:runner than 0.5 is available: 1.0.1
and espresso-core implementation is highlighted with following hint:
A newer version of com.android.support.test.espresso:espresso-core than 2.2.2 is available: 3.0.1
QUESTION 1- I have SDK tools versions 27.0.0 and 27.0.1 and 27.0.3 installed on my system. Why android studio uses 26.0.0-alpha1 as a default which causes error?
QUESTION 2- How can I change this default to proper 27 version?
When I try changing compileSdkVersion and targetSdkVersion to 27 and changing appcompat version to v7:27.0.0 then I come up with following errors after syncing:
image description
QUESTION 3- Why this error is happening and how to rectify it?
I revert back to SDK 26 and try to upgrade test:runner and test.espresso:espresso-core to what android studio suggests. It ends up with this error:
image description
QUESTION 4- Why android studio cannot resolve the upgrading which it suggests?
QUESTION 5- What is a sample working gradle build configuration using latest SDK version (27)?

Answer 1

After too many investigations, I regretfully found that all errors were due to unfair sanctions by Google against my country's people (not against the government as they claim!).
My Android Studio was not able to contact jcenter and maven repositories.
After using a VPN program everything was settled and all errors were vanished!!