Backfilling is the right one
Answer:
a. Scott does not like feeling sweaty, so he rarely does any moderate or vigorous physical activity--- Individual factor
b. Kirstin's new boytriend loves to salsa dance, and now she goes out dancing with him two nights a week--- Environmental factor
c. Brian eats mostly fast food because there is not a grocery store close to his apartment--- Environmental factor
d. Tanya never saw her parents have a disagreement and, as a result she avoids conflict in her close personal relationships--- Environmental factor
e. Dave has hated green vegetables since he was three years old--- Personal factor.
The most widely accepted theory of planetary formation, known as the nebular hypothesis, maintains that 4.6 billion years ago, the Solar System formed from the gravitational collapse of a giant molecular cloud which was light years across.