MULTIPLE CHOICE (identify the one best answer below and explain your reasoning for each option): The so-called 'grey' or 'underground' economy production is sometimes not included in the GDP calculation because:

a. Many politicians smoke marihuana and do not want us to know about it.

b. Workers like avoiding taxes when paid cash-in-hand.

c. The associated transactions are not recorded so no reliable data exist.

d. All of the above

e. None of the above.

Please do not provide same answers.