Answer:
Through the actions of Stanley's dad.
Step-by-step explanation:
Louis Sachar's book "Holes" revolves around the tale of how children were kept in a camp and made to do manual labor with the secret intention of looking for "something". The children were not privy to their objective, but just that they were supposed to keep on digging. But through the development of the story, the young protagonist Stanley Yelnats discovered who a true friend is.
As given in the excerpt, the narrator/ author states that "Stanley's father was smart and had a lot of perseverance". This perseverance and endurance can be seen in his actions, how "Once he started a project he would work on it for years, often going days without sleep".
Thus, the correct answer is the second option.