Refer to the Figure

Multiple Choice

Refer to the figure.
The RNE (relative neighbor effect) measures growth of a target plant species in the presence and absence of neighboring species. The figure shows graphs of the RNE at eleven sites around the world. RNE was measured at high and at low elevations at each site. RNE values above zero (blue) indicate that neighboring plants increased the growth of target species; RNE values below zero (red) indicate that neighbors decreased target species growth.
-This study showed that the presence of neighboring plants most often benefited the target plants at

A) high-elevation sites.
B) low-elevation sites.
C) sites in North America only.
D) sites in Europe only.