Consider the following graph that illustrates two production possibilities frontiers Which of the following could have caused the production possibilities frontier to shift from PPF2 to ppFt ? C) There is a decline in the number of people willing and able to work in the bicycle industry. C) New farm equipment allows the fields to be harvested more quickly. C) There is an increase in the of people available to work. C) New machines are installed in the bicycle factory that replace 20% of the workers.