Detail

6. Notice that PPFs B and A intersect the vertical (good 2) axis at the same point. If all resources are used to produce good 2 it doesn't matter which PPF we're on, the same amount of good 2 can be produced. However, on PPF A, if all resources are being used to produce good 1, much more can be produced than on PPF B. Thus, either the technology for producing good 1 has improved (the correct answer) or more resources useful only in producing good 1 have been acquired (not a choice, but it would also have been correct if it had been an available choice.)