As a measure of well$-$being, GDP tends to:

c$.$ Understate economic well$-$being because it does not take into account improvement in product quality and leisure

a$.$ Overstate economic well$-$being because it does not include certain non$-$market activities such as the productive work of volunteers

d$.$ Overstate economic well$-$being because it includes the underground economy

b$.$ Understate economic well$-$being because it includes expenditures undertaken to offset or correct pollution