figure 3 below shows a non-linear version of a PPF for a country that produces cell phones and tractors

Cell phones K tractors Figure 3 What describes the reason that the PPF in Figure 3 looks different than the PPFs in Figure 2 above? This figure assumes that one good is easier to produce than the other This figure assumes that the opportunity cost of the two goods are equal to each other This figure assumes that this economy is producing more than two goods This figure assumes that the resources in this economy differ in productivity for each good