Intrinsic motivation is a motivation "from inside", with internal, rather than external awards.
Three of the things you mentioned have an external reward: the 500 Dollar prize( first option), the credit (third) and the hope of winning a blue ribbon (the last).
Only the second one has an intrinsic motivation: that you will be happy about performing this song (feeling proud of yourself, etc).
I believe that the phrase from Mandela's speech that is an example of a metaphor is the first one - 'the children, [...] the greatest of our treasures."
A metaphor is a type of comparison, where two or more things are compared without using words such as <em>like </em>or <em>as. </em>Here, the children are the greatest of our treasures - they are compared to a treasure, something which is the most important thing of all.
All falls under indefinite.
The answer to the question is b
I believe the answer is A. Hope I helped!
