1.
it was a series of separate walls
“extending” across northern China.
想問為什麼不用被動extended
2.
I'll finish it later “on”.
請問on是慣用語還是有其他說明跟解釋
謝謝大家

1. 牆本身一直延展出去，不是被某人延展。2. later on跟later基本上可互換。