stepping stone
noun
1- a raised stone used singly or in a series as a place on which to step when crossing a stream or muddy area（小溪、泥泞地的）踏脚石。
1.1
- figurative an undertaking or event that helps one to make progress towards a specified goal〈喻〉垫脚石：
the school championships are a stepping stone to international competition.
学校的锦标赛是进入国际比赛的垫脚石。