A child can be a reliable source because children are so young and pure, their views usually are not biased and they just tell the story like they see it.
This part of the thesis would be considered the topic, more specifically it would be considered the <em>introduction of the topic to study</em> since the thesis revolves around, I assume, Isaac Newton and you are offering a brief 'summary' of his life and accomplishments.
However if the reason to mention Sir Isaac Newton is to support an idea or a statement this could be considered a subtopic. It is subjective and directly related to the field of study you're doing the thesis for.
Hope this helps!
Answer:
whose.
Explanation:
Mountain gorillas are an endangered species whose habits are being badly destroyed.
