Critical Reasoning

The chanterelle, a type of wild mushroom, grows beneath host trees such as the Douglas fir, which provide it with necessary sugars. The underground filaments of chanterelles, which extract the sugars, in turn provide nutrients and water for their hosts. Because of this mutually beneficial relationship, harvesting the chanterelles growing beneath a Douglas fir seriously endangers the tree.
Which of the following, if true, casts the most doubt on the conclusion drawn above?
(A) The number of wild mushrooms harvested has increased in recent years.
(B) Chanterelles grow not only beneath Douglas firs but also beneath other host trees.
(C) Many types of wild mushrooms are found only in forests and cannot easily be grown elsewhere.
(D) The harvesting of wild mushrooms stimulates future growth of those mushrooms.
(E) Young Douglas fir seedlings die without the nutrients and water provided by chanterelle filaments.