Machine Learning is a particular approach within the field of Artificial Intelligence.

a$.$ What is a defining characteristic that distinguishes machine learning from non$-$machine learning AI approaches?

b$.$ Imagine a medical diagnostic tool that can scan an image of a brain tumour, and detect whether the tumour is benign or malignant. Describe, in general terms, how we might use machine learning to develop this tool.

c$.$ Why might it be difficult to develop this tool without using machine learning?