Great Basin National Park, the Only National Park Wholly Within

Great Basin National Park, the only national park wholly within the borders of Nevada, occupies 77,180 acres and contains 42 known caves.About 90,000 people visit the park each year.It has 25 permanent staff who, with the seasonal staff, collect $280,00 in fees a year, mostly for the 2,400 cave tours.The park also has about 80 volunteers who contribute 9,400 hours of work a year.Because the park suverys for springs in the 25 watersheds, the park service does not burning any acreage, which is part of standard maintenance in some parks. Some of the data in this paragraph are flow measurements and some are stock measurements.An example of a flow measurement is:

A) staff positions in the park.
B) acres in the park.
C) cave tours given.
D) caves in the park.