Question:
The advisor told the President that he was resigning.

he
Answer:
The advisor
Question:
The music player did not open the file because it was in the wrong format.

it
Answer:
the file
Question:
The mechanic charged the man one hundred dollars although he had done no work.

he
Answer:
The mechanic
Question:
John hit Carl and he did not like it.

he
Answer:
Carl