under which condition least likely to earn economic rent

under which pair of conditions is a factor of production least likely to earn economic rent? Supply curve Demand Curve A Upward Sloping Downward Sloping B Upward Sloping Perfectly Elastic C Perfectly Elastic Perfectly Elastic D Perfectly Elastic Downward Sloping I appreciate very much your time!

When the Supply curve is perfectly elastic (completely horizontal, ie. nonrenewable sources) and the Demand is downward sloping, the area below the S and D curve is 100% opportunity cost and 0% rent.

Many thanks CFA-2010