Advertisement: Most power hedge trimmers on the market do an adequate job of trimming hedges, but many power hedge trimmers are dangerous to operate and can cause serious injury when used by untrained operators. Bolter Industries' hedge trimmer has been tested by National Laboratories, the most trusted name in safety testing. So you know, if you buy a Bolter' s, you are buying a power hedge trimmer whose safety is assured. The answer to which one of the following questions would be most useful in evaluating the truth of the conclusion drawn in the advertisement? ["What were the results of National Laboratories' tests of Bolter Industries' hedge trimmer?", 'Has National Laboratories performed safety tests on other machines made by Bolter Industries?', "Does any other power hedge trimmer on the market do a better job of trimming hedges than does Bolter Industries' hedge trimmer?", 'How important to the average buyer of a power hedge trimmer is safety of operation?']