private async Task<string> GetGreetingAsync()
{
    return await Task.Run(() => "Hello");
}

private void button1_Click(object sender, EventArgs e)
{
    var x = GetGreetingAsync().Result;
}

private async Task<string> GetGreetingAsync()
{
    return await Task.Run(() => "Hello").ConfigureAwait(false);
}

private void button1_Click(object sender, EventArgs e)
{
    var x = GetGreetingAsync().Result;
}

private async Task<string> GetGreetingAsync()
{
    return await Task.Run(() => "Hello");
}

async private void button1_Click(object sender, EventArgs e)
{
    var x = await GetGreetingAsync();
}

private Task<string> GetGreetingAsync()
{
    return Task.Run(() => "Hello");
}

async private void button1_Click(object sender, EventArgs e)
{
    var x = await GetGreetingAsync();
}

private async void button1_Click(object sender, EventArgs e)
{
    var x = await GetGreetingAsync();
}

private async Task<string> GetGreetingAsync()
{
  return await new Task<string>(() => "Hello");
}

private Task<string> GetGreetingAsync()
{
  return new Task<string>(() => "Hello");
}