Is often considered the "dispensable" sense, the one we could most easily live without if necessary.

The answer is A) Smell

Smell is an important sense and one which actually enables us to feel the environment and even helps to actually taste our food. 
It has been proven that if we cannot smell our food, the taste will be quite different.

However, the senses of Hearing, Vision and Touch are actually far more important in order for humans to go about their daily lives.

Without smell, any human can still live with a healthy life with good cognitive control and intelligence. 

The same cannot be said about Hearing, Vision and Touch.