In the typical production possibilities model, a shift of the entire production possibilities curve is caused by a change in
technology that only affects the production of the good on the x-axis
technology that only affects the production of the good on the y-axis
the availability of scarce resources needed for production
the price of goods related to the those included in the model

the availability of scarce resources needed for production

Explanation:

The production possibilities frontier model - PPF shows how much an economy can produce of two different products typically showing production goods such as machinery and consumption goods as donuts, there is a tradeoff between the products along the curve and any point in which this trade off occur is efficient.  

The only ways to shift the curve outward or inward is by a change on technology that affect both of the goods, by trade, or by the availability scarcity of the resources needed to produce. those goods

the correct choice is a