fledging <> mature

flee <> plodding

flexibility <> calcification

flexible <> mulish

flippancy <> grave

flippancy <> seriousness

flippancy <> sobriety

flippant <>    reverential

flippant <> earnest

flit <> plod

flock <> segregate

florid <> solemn

flounder <> act gracefully

flounder <> slide

flourish <> waste away

无经验的  <> 成熟的

逃避  <> 重步走

灵活  <> 僵化

灵活的  <> 顽固的，执拗的
轻率  <> 严肃

轻率  <> 认真

轻率  <> 严肃

轻率的  <> 尊敬的沮丧的

轻率的  <> 认真的

迅速飞过  <> 缓慢移动

聚集  <> 隔离

鲜艳的  <> 严肃的

挣扎  <> 优雅的运动

挣扎着前进  <> 滑动