Which of the following is a correct statement about the production of shale oil in the u. s.?

question 8 options:

a)

if petroleum becomes more expensive due to dwindling supplies, shale oil use still won't be economically feasible since it is so expensive to produce.

b)

development of new technology that reduces the cost of extracting shale oil is impossible due to environmental dangers.

c)

if political factors make petroleum expensive or impossible to obtain, the use of shale oil might increase.

d)

shale oil is an abundant resource and it is currently less expensive than petroleum to produce, but is not widely used.