Trevor Is Trying to Solve an Open-Ended Physics Problem

Trevor is trying to solve an open-ended physics problem. First, he first gathers all of the necessary information before he tackles the problem. Once that part is complete, he tries to come up with different ways to solve the problem. After about 45 minutes of working on the problem and coming up empty-handed, he decides to go for a nice long walk with his dog. About 20 minutes later, just as he approaches his apartment, he gets an idea of how he might solve the problem. He runs inside and applies his idea to the problem. Finally, the physics problem is solved. In which part of the scenario did Trevor experience incubation?

A) when he got an idea to solve the problem as he was approaching his apartment
B) when he went to walk his dog
C) when he applied his idea to the problem
D) when he gathered all of the necessary information