In a Laboratory Experiment, Researchers Treated Pine Seedlings from Puerto

In a laboratory experiment, researchers treated pine seedlings from Puerto Rico with mycorrhizae collected from pine forests in the southeastern United States. Results were favorable for increased seedling growth in the trees treated with mycorrhizae. Suppose when the researchers then tried this same experiment in the field, pine tree seedlings treated with mycorrhizae showed minimal growth differences from the control group. All but one of the listed factors could have contributed to these results. Choose the exception.

A) Researchers in the lab provided greater nutrient concentrations to the two groups of trees.
B) Weather conditions in the field were not favorable for tree growth whereas the laboratory environment provided ideal growing conditions.
C) Mycorrhizae in the laboratory functioned separately from the plant roots.
D) Researchers planted a large number of seedlings in the laboratory but only a minimal number in the field, so their sample size in the field was not large enough to show a possible effect.