alternation
noun [ S or U ] uk/ˌɒl.təˈneɪ.ʃən/ us/ˌɑːl.tɚˈneɪ.ʃən/
轮流，交替
a situation in which one thing repeatedly happens or exists after another
Flowers and trees are planted to produce an attractive alternation of light and shade in the garden. 种植鲜花与树木以期在花园里营造光影婆娑的动人景致。