According to the graph above, the population gap between the united states and japan is a. widening b. shrinking c. unchanging d. undetermined

The correct answer is - A. widening.

Both of the countries suffer from low fertility rate, Japan little more than the USA. The gap is widening because of the migrations.
- USA is country that is on the top of the list as a destination for migration, and also it is a country that allows big number of migrants in it every year, that contributes to the country's population to become bigger and bigger even though the fertility rate is low.
-Japan the other hand is a country that has both very low fertility rate, and very small amount of migrants coming to live in it, so the number of the population is stagnant for some time now, and is expected to start decreasing quickly in the coming years once the older population is not among the living anymore.