Final answer:
The difference in behavior between Matt and Steven can be best explained by their different temperaments. Matt shows a reserved and cautious temperament, whereas Steven displays an outgoing and explorative one.
Step-by-step explanation:
The difference in behavior between Matt and Steven, two kindergarten children, can be best explained by their differences in temperament.
Temperament refers to inborn, genetically based personality differences that influence how one acts and responds to the world from a very young age, including their activity level. While Matt seemingly has a temperament that is more reserved and cautious, Steven exhibits a more outgoing and explorative temperament.
Temperament shapes how children experience and react to the world, including their emotional reactivity and their ability to self-regulate in response to new or challenging stimuli.
Therefore, the most suitable answer to the student's question is C. temperament.