上升:rise/increase/improve/climb/soar/go up/put up/peak at/reach a peak/reach a summit/shoot up/pick up/be on the rise/be up/an upward trend
下降:drop/decrease/fall/reduce/decline/plunge/collapse/plummet/do down
其他:平稳remain/stay/stable 下降后平稳bottom out 上升后平稳level off 恢复recover/bounce back 波动fluctuate/vary
程度:sharply/dramatically/considerably/substantially/significantly/remarkable/rapidly/noticeable/slightly/gradually/smoothly/steadily/sloely/constantly