Answer: the world price of the good on the horizontal axis.
Explanation:
The Consumption Possibilities Curve (CPC) is much like the Production Possibilities Curve (PPC) except that the PPC represents the combinations of two goods that can be produced and consumed when a country is not trading but CPC represents that same measure when there is trade.
In the CPC graph, the world price of the good is represented on the horizontal axis to show the prices of the goods on the world market vs the quantity that can be acquired.