In preparation for a large-scale tree-planting project, Thomasville has recorded the location, species, and condition of every tree in its downtown area. The results will be compared with results of the last such tree census, taken 20 years ago. Planting trees primarily from the species that turns out to have the best record of survival will assure downtown Thomasville of an abundant tree population 20 years from now.

Which of the following, if true, most seriously undermines the claim that the tree-planting proposal will assure an abundant tree population?

【选项】A city with a high proportion of any one species of trees can have its tree population devastated by one outbreak of a disease.