Ruby on Rails

Hi Rails developers,

I would appreciate some assistance. Please study the following code and provide your reasoning for whether you agree or disagree with the following statements. 

I understand the code is not specific to Rails, however I am specifically interested in Rails developer's perspective. Thanks!

car.rb

class Car
 def initialise(engine)
   @engine = engine
 end

 def start
   @engine.start
 end
end

engine.rb

class Engine

 def start

   puts 'Engine started'

 end

end

- Car is not dependent on, and therefore not coupled to Engine

- Car is dependent on an object that responds to "start"

- Car may or may not be initialised with an Engine object

- Car uses constructor-based dependency injection