Of the following examples, which would you address using an unsupervised learning algorithm?
a. Given email labeled as spam/not spam, learn a spam filter.
b. Given a set of news articles found on the web, group them into sets of articles about the same stories.
c. Given a database of customer data, automatically discover market segments and group customers into different market segments.
d. Given a dataset of patients diagnosed as either having diabetes or not, learn to classify new patients as having diabetes or not.