transient

夏日午后的阵雨带来一丝清凉，但这种舒适感转瞬即逝。

The summer afternoon shower brought some coolness, but the comfort was ___transient.

户外市场短暂聚集的人潮在雨一开始下时就四散离开了。

The ___transient crowds at the outdoor market thinned out as soon as the rain started.

童年夏天的记忆总是如此鲜活，却又如此短暂易逝。

Memories of childhood summers always felt so vivid, yet so ___transient.