The correct answer is tick on a dog.
The parasitic relationship can be defined as the relation in which one organism feeds on the other organism for their nutritional purpose. It can also harm the other organism by any means. Here, tick on the dog is dependent on the dog for its nutritional requirement. This is an example of parasitic relationship between dog and tick.
I don't know about the other ones but the sky is blue because molecules move from the sun than the red from the sun. The blue has separated from the sun.
