Unit 2: Inflation: Changes in the basket of goods

The BBC reports the annual changes in the basket of goods used to measure the CPI

http://news.bbc.co.uk/1/hi/business/7958785.stm

a) What is the CPI?
b) Why do the articles in the basket of goods alter?
c) Would you have expected the weights allocated to the various items in the basket to have changed this year? Explain your answer