Explanation

Phone me after 8 'Clock  I'll have finished dinner by them

مجھے 8 بجے کے بعد فون کریں میں ان کے ساتھ رات کا کھانا ختم کر لوں گا۔

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The future perfect is a verb tense used for actions that will be completed before some other point in the future.

It is for talking about an action that will be completed between now and some point in the future.

Here, the action of the dinner will be completed before a specific point of time 8:00.

Hence, Option B is correct

ND13-07-2023