David Blehert and his research team captured 117 healthy bats to study in the laboratory and divided them into four groups. Group 1 was housed in an area free from Geomyces destructans. Group 2 was housed in an area that shared the same air as bats infected with WNS, but these bats did not have direct contact with the infected bats. Group 3 was housed in direct contact with other bats infected with WNS. Bats in group 4 were directly exposed to Geomyces destructans when researchers applied it to the bats’ wings. During the study period the bats were monitored for signs of WNS. What is the specific hypothesis being tested by the inclusion of group 4 in this experiment?