The sentence that correctly uses the word "principal" is the second sentence. The word "principal" refers to the person who has the highest authority in an institution, particularly as referred here, which is a school. On the rest of the sentences, the right word to be used is "principle" and not principal.
Oisin. His name literally means young dear. In this story, told by his mother, he was turned into a dear by a druid.<span><span><span> </span></span></span>