Which of the options best fits gap 15?

Directions: Complete the gaps with a suitable option from the given ones to form meaningful sentences.

Communication is----11--- important as food and clothing. They are needs not wants. Not only human beings but also animals and birds communicate in their own language. Animals communicate -------------12----------gestures, cry and fondling which --------13----non verbal. The nature of communication can be approached ---------14------ huge variety of functional and structural perspectives. A communication channel must have -----15------encoder and a decoder. The medium ---------16---------the code.