The correct answer is D.
OBJ-4.2: Avoid using actual times instead of points when estimating. Points are arbitrary and therefore reduce the likelihood of problems and potential for conflict. Agile uses empiricism to estimate, rather than rationalism. There are many variations of numbering systems used as part of agile estimating and most are based on the Fibonacci sequence. The most common form of relative estimation is achieved by giving requirements or user stories a points value that means something relative to another requirement or user story. Another very popular estimating technique is called T-shirt sizing.