The correct answer is D) toothpaste and toothbrush.
What is not an example of substitute goods are toothpaste and toothbrush.
In economics, when we are talking about substitute goods we are referring to two alternative goods that could be used for the same reason or purpose.
In the case of this question, you cannot substitute the toothbrush for the toothpaste. You need the two together to brush your teeth. You can do it with one or the other. In the other options, yes, you can substitute margarine for butter or a motorcycle for a car, both are means of transportation.
