visitors have been asked to keep the woods clean and tidy.为什么要用have been asked？

Question

和 visitors were asked to keep the woods clean and tidy. 有什么不一样吗？

Answer 1

做为公告启示这当然是用 have been asked = are required ，只是asked 意思不一样的。
visitors have been asked to keep the woods clean and tidy ，= 访客必需保持森林区内清洁和整齐。
visitors were asked.....访客曾经被要求保持森林区清洁整齐，是个事故报告，做告示是不成立。

Answer 2

Somebody have/has been asked用现在完成时的被动语态表示已经被要求过了，要是过去已经发生过的事，Were asked只能表示过去式过去发生的事没有对现在的影响，因为Visitors游客是被管理者要求的所以使用被动语态。追问

have been asked 是强调“已经！”被要求过了，be asked就感觉只是随随便便被要求过了而已。能这么理解吗？

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Answer 3

您好，句中have been asked是被动语态哦。
句意:游客被要求保持森林干净整洁 。

Answer 4

Visitors have been asked to keep the woods clean and tidy.

是现在完成时态的被动语态。

visitors were asked to keep the woods clean and tidy.
是一般过去时态的被动语态。