For years, a rare variety of camel was endangered because much of its habitat was used as a weapons testing range. After the testing range closed, however, the population of these camels began falling even more quickly. Which one of the following, if true, most helps to explain the increased rate of population loss? ['The weapons tests had kept wildlife poachers out of the testing range.', 'Because of unexploded bombs, the land within the testing range was still somewhat dangerous after the range closed down.', 'The weapons tests were most harmful to the camels in years when food was scarce.', 'The camels had to overcome two different outbreaks of disease during the time the testing range was in operation.']