AsyncInOverride.cs

void Main()
{
    var instances = new AbstractBase[]
    {
        new RegularTaskApproach(),
        new AsyncAwaitApproach(),
        new RegularTaskDerivedFromAsyncAwaitApproach(),
        new RegularTaskUsingBaseAsyncAwaitApproach(),
    };
    
    var results =
        from instance in instances
        let task = instance.DoSomethingAsync()
        select new
        {
            instance.GetType().Name,
            task.Result,
        };
        
    Console.WriteLine ("Results:\n{0}", String.Join("\n", results));        
}

// Define other methods and classes here
public abstract class AbstractBase
{
    public abstract Task<string> DoSomethingAsync();
}

public class RegularTaskApproach : AbstractBase
{
    public override Task<string> DoSomethingAsync()
    {
        return Task.Factory.StartNew(() => "i'm a regular task");
    }
}

public class AsyncAwaitApproach : AbstractBase
{
    public override async Task<string> DoSomethingAsync()
    {
        return await Task.Factory.StartNew(() => "i used await!");
    }
}

public class RegularTaskDerivedFromAsyncAwaitApproach : AsyncAwaitApproach
{
    public override Task<string> DoSomethingAsync()
    {
        return Task.Factory.StartNew(() => "i'm a regular task derived from async impl");
    }
}

public class RegularTaskUsingBaseAsyncAwaitApproach : AsyncAwaitApproach
{
    public override Task<string> DoSomethingAsync()
    {
        var taskFromAsyncParent = base.DoSomethingAsync();
        var taskAddingOnSomething = taskFromAsyncParent
            .ContinueWith(t => t.Result + " ... and i helped!");
            
        return taskAddingOnSomething;
    }
}