One day a rich father took his young son_ a trip to the countryA.in B.for c.at d.on 说明理由

One day a rich father took his young son_ a trip to the countryA.in B.for c.at d.on 说明理由
One day a rich father took his young son_ a trip to the countryA.in   B.for  c.at   d.on 说明理由

One day a rich father took his young son_ a trip to the countryA.in B.for c.at d.on 说明理由
on
on a trip to.是固定搭配,去某地的旅途中

选d
on a trip to...是固定搭配
on a trip to...在去...的途中