The answer is
Yet.
A coordinated conjuction is a word that joins or coordinates two senteces together, in this case the word yet is conectint he was but a child, and giving meaning to the whole sentece by conecting to he did so much for others, if you read it without the yet, the sentence looses force in the statement.
Kylie had 4 chocolate bars and she gave each one of her friends one, they were all happy but there was a problem, Kylie didn’t have one for her.
Answer:
they
Explanation:
because they is the 3 rd person spoken as a plural form nominative - subject before the action verb ; after lingking verb