An experiment is conducted on the effects of trampling on vegetation in alpine meadows. a 70-kilogram hiker wearing heavy boots will be used. twenty sections of vegetation, each 0.5 by 4.5 meters, are divided up into 5 groups. the hiker will walk on each section 0, 25, 75, 200, or 500 times. after 1 year, the height of the vegetation in each section is measured. is there a control group?

a. yes, because the same hiker is used throughout the experiment.
b. no, because all sections have vegetation to start.
c. yes, because some sections get 0 walking passes.
d. yes, because sections are all the same size.