What Defines Flexible Resources

What defines flexible resources?

A) A change in resource spending will occur only if the demand for a resource drops permanently and exceeds demand enough so the activity capacity will be reduced.
B) Often,resources are acquired in advance for multiple periods and are therefore irrelevant.
C) Decisions often affect multi-period capabilities.
D) If the demand for an activity changes across alternatives,then resource spending will change and the cost of the activity will be relevant to the decision.