С: нужно преобразовать глагол в конце предложения по смыслу. as he sat thinking to himself about what for his lunch,he heard a voice call out to him from bottom of the tree. go

Going - As he sat thinking to himself about what he going have for his lunch,he heard a voice call out to him from bottom of the tree.

Went to. As he sat thinking to himself about what he went to have for his lunch,he heard a voice call out to him from bottom of the tree. Просто Past Simple, на это даже указывает следующая фраза "he heard"