Question

we all know that mobile phone has greatly facilitated our oral communication system (make passive)

Answer 1

Answer: It is known to all of us that our oral communication system has been greatly facilitated by mobile phone.

Explanation: We have 3 objects here, We, Mobile Phone, and Communication System.

Keeping the first object same, we replace the 2nd object by 3rd and 3rd by 2nd. Then, to keep the meaning same, we have to change the first phrase, therefore "We all know" becomes "It is known to all of us"

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