The practical thing was to find rooms in the city, but it was a warm season, and I had just left a country of wide lawns and friendly trees, so when a young man at the office suggested that we take a house together in a commuting town, it sounded like a great idea. He found the house, a weather-beaten cardboard bungalow at eighty a month. Nick’s recent arrival at West Egg and his intention to stay for only a short time underscore the fact that
he is not as wealthy as his counterparts.
he has just returned from the war.
he is being supported by his family.
he is an outsider in this community.

That's why he opened the Apache Agency Skate Shop. It's a social hub for skaters on the reservation. The shop organizes skate competitions and concerts. It also sponsors a team of talented skaters who travel around giving skating demonstrations. Skateboarding is paving the way for a new generation of Native American leaders.  

Explanation:

The option shown above shows what Douglas Miles did that motivated the skateboarding culture in the Apache reserve of San Carlos, that is, this passage supports the statement because it presents facts that prove the influence of Douglas Miles and helps him to keep this culture active and operating within the reserve.

In other words, we can say that Douglas Miles' influence comes from maintaining the skateboarding culture and providing resources for those who wish to practice it.