The high population density of modern japan has led to
a. environmental issues
b. many poor neighborhoods
c. urban sprawl
d. efficient public transport

B. Many Poor Neighborhoods.

Explanation:

Although some would argue that urban sprawl has its benefits, such as creating local economic growth, urban sprawl has many negative consequences for residents and the environment, such as higher water and air pollution, increased traffic fatalities and jams, loss of agricultural capacity, increased car dependency, ...

If i am Wrong let me know right away.

because the center-south is called the heart of the country