Which of the following statements is accurate about most economies?

A. Economies experience a positive growth trend over the short run but experience significant variability in the long run.
B. Economies experience a positive growth trend over the long run but experience significant variability in the short run.
C. Economies experience positive and stable growth over both the long run and short run.
D. Economies experience little long-run growth in output but can experience significant growth in the short run.