Ecologists have studied the four chipmunk species ...
Ecologists have studied the four chipmunk species that occur on the eastern slope of the Sierra and have learned just how these species interact while remaining separate, each occupying its own elevational zone. The sagebrush chipmunk is found at the lowest elevation, among the sagebrush. The yellow pine chipmunk is common in low to mid-elevations and open conifer forests, including pinon and ponderosa and Jeffrey pine forests. The lodgepole chipmunk is found at higher elevations, among the lodgepoles, firs, and high-elevation pines. The alpine chipmunk is higher still, venturing among the talus slopes, alpine meadows, and high-elevation pines and junipers. Obviously, the ranges of each species overlap. Why dont sagebrush chipmunks move into the pine zones？ Why dont alpine chipmunks move to lower elevations and share the conifer forests with lodgepole chipmunks？
Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 4？ Incorrect choices change the meaning in important ways or leave out essential information.
A．Ecologists studied how the geographic characteristics of the eastern slope of the Sierra influenced the social development of chipmunks.
B．Ecologists learned exactly how chipmunk species separated from each other on the eastern slope of the Sierra relate to one another.
C．Ecologists discovered that chipmunks of the eastern slope of the Sierra invade and occupy higher elevational zones when threatened by another species.
D．Ecologists studied how individual chipmunks of the eastern slope of the Sierra avoid interacting with others of their species.