Bit stuffing refers to inserting a 0 in user stream to differentiate it with a flag.
Each frame begins and ends with a special bit pattern called a flag byte ex. 01111110.
Whenever sender data link layer encounters five consecutive ones in the data stream, it
automatically stuffs a 0 bit into the outgoing stream.
When the receiver sees five consecutive incoming ones followed by a 0 bit, it automatically
destuffs the 0 bit before sending the data to the network layer.
Option A is correct.