TPO10 Varuations in the climate - 英檢

插入句題13: Indeed, the contribution of volcanoes and solar activity would
more likely have been to actually reduce the rate of warming slightly.
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請問這句為何要用have been to V呢?

為何不用 ....more likely to (actually) reduce the...現在式
或 more likely have reduced the..... 完成式

我在我的文法書上也找不到 have been to V的用法
(只有曾經去過某地,這又好像不是)

謝謝..
(解題好像沒什麼問題)

Pa. 7 : Inaddition to the internal variability of the global climate system
itself, there is the added factor of external influences, such as volcanoes a
solar activity. █ There is growing body of opinion that both these phsical
variations have a measurable impact on the climate. █ Thus we need to be abl to include these in our deliberations. █ Some current analyses conclude that
volcanoes and solar activity explain quite a considerable amount of the
observed variability in the period from the seventeenth to the early twentiet
century's, but that they cannot be invoked to explain the rapid warming in
recent decades. █

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