Answer:
A) meaning
Explanation:
The crucial element of communication is the meaning of what is trying to be communicated. For example, how many times do we want to express some idea, but we cannot use the proper words or the person to whom we are talking to doesn't understand what we are trying to say? Or how many times does your teacher tell you something and you do not understand what he/she is saying?
The other elements are relatively simple and easy to understand and carry out in normal life: