不能去掉,with which 做方式状语 we travelled with the ballon【which代替the ballon】如果去掉 the ballon we travelled was filled with hot air.这样句意不通.the ballon 和 we travelled无法连接翻译：我们旅行...这里的which是定语从句的连接词还是从句部分的宾语是定语从句的连接词，而且在定语从句中做宾语