The underlined structure in the excerpt “the reasons behind ...

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The Bizarre Story of the Swedish Warship “Vasa”

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(Available at: https://www.smithsonianmag.com/smart-news/bizarre-story-vasa-ship-keeps-giving-180964328/ – text especially adapted for this test). 
The underlined structure in the excerpt “the reasons behind the instability have remained a point of debate over the centuries” (l. 11-12) is in the present perfect tense. Considering this verb tense uses and the context in the article, we can say the action is/was: 
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