Hello, Mandalou7124. Thanks for writing in.
You asked: In ____ communication schemes the sender and receiver are linked and ready to send and receive.
From that problem, you are asking to fill in the blank.
The answer that goes in the blank is Synchronous.
You would rewrite it like: In synchronous communication schemes the sender and receiver are linked and ready to send and receive.
Synchronous is like something is occurring but something else is happening at the same time. In this case, they are ready to send and receive.