What Is the Basic Problem or Issue with Respect to Expanding

Multiple Choice

What is the basic problem or issue with respect to expanding the world's oil supply in the future?

A) all of the answers listed here
B) fewer giant fields are being found today
C) numerous smaller fields must be found to offset production declines in older fields
D) remaining deposits are more expensive and difficult to extract
E) discoveries of new fields peaked in the 1970s