Petroleum, a Relatively Cheap Nonrenewable Energy Source, Is

Petroleum, a relatively cheap nonrenewable energy source, is:

A) in abundant supply but is not environmentally clean.
B) being increasingly depleted and is expected to run out in another 50 years, but in the meantime, improved retrieval techniques are being developed.
C) clean, cheap, and available, but most of the reserves are located in countries whose leadership is critical of the industrialized world.
D) expected to run out in another 10 years and needs to be replaced with renewable energy sources quickly.