very very easy English

can I use jiust have (verb（present prefect tense))


Yes. but they have different meanings.
I just have finished high school" 我剛好完成了高中/我只是完成了高中
I have just finished high school" 我剛剛完成高中Just : [副詞] 正好, 恰好, 僅僅, 只是, 剛剛e.g. That is just what I want to know. 那正是我想知道的。He is just a child. 他只是一個孩子。He is just out of hospital. 他剛剛出院。

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yes!! have just (verb（present prefect tense))