請問這兩句英文句子有何不同？

The policy will be carried out. ( simple future tense)
We know that the policy will be carried out, but we do not know WHEN it will be carried out.
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The policy is to be carried out.= The policy should be carried out.

"to be" here is used as " SHOULD".
The verb to be in this sentence acts as an auxiliary verb to extend a sense of obligation or duty to the observer.

Examples:
Alaslee80 has taught me how to use " to do". (Present perfect tense)

Alaslee80 has TO BE TAUGHT how to use "to do".<----(present tense)
Alaslee80 should be taught how to use " to do".
Can you tell the difference now?

Hope that helps.

Ciao

你好，你所提供的两句都是被动式 (Passive Voice) 的句子，但我为你找来主动式 (Active Voice) 的结构来解释的。
请看 http://hk.knowledge.yahoo.com/question/question?qid=7007110509498
以上的网址有提到主动式的结构 (will + verb 和 am/is/are to + verb) 所含有的稍微不同的意思与语气咯。
两句都是讲述着未来的事情，也有已被安排好的意思，但是 The policy will be carried out. 也可以说是“临时或现在才下决定”的意思。反而 The policy is to be carried out. 是讲述着“已定的计划或早已被安排好”的意思，语气也最为强烈的咯。
希望能帮到你咯。。。: )

第二句是比較肯定一些，即是說這政策一定會執行。

兩句沒有太大的分別如cxm...所講
但是第二句就比較似命令（order），而第一句就似普通的報告。

希望幫到你！

沒有分別..兩個都係將來式