(a) What is underground economic activity? How does it affect the measure of the true size of an economy? (11 marks) (b) How does the production of a Hong Kong firm in Mainland China affect Hong Kong's GDP and GNP? (11 marks) (c) \"If Country A has a higher level of real GDP per person than Country B, then citizens in Country A must enjoy a higher standard of economic welfare than citizens in Country B.\" Do you agree or disagree this statement? Why? (11 marks)