Over time, people have come to rely more on market-produced goods and services and less on goods and services they produce for themselves. For example, busy people with high incomes, rather than cleaning their own houses, hire people to clean their houses. By itself, this change has

a. caused measured GDP to fall.
b. not caused any change in measured GDP.
c. caused measured GDP to rise.
d. probably changed measured GDP, but in an uncertain direction; the direction of the change depends on the difference in the quality of the cleaning that has resulted.

c