一起一落to rise and fall

• 波涛起伏

  waves roll

• 岗峦起伏

  hills roll

• 岗峦起伏的地区

  area of rolling hills

• 病情起伏

  the illness comes and goes

• 两国关系出现了一些起伏。

  Relations between the two countries have entered a bumpy patch.

【理】fluctuation