6.Within the foreseeable future there may be a major ______ of species, involving from one-third to two-thirds of all the species now in existence.
A. exhaustion
B. exhibition
C. extension
D. extinction
选项解析：
A. exhaustion 筋疲力尽
B. exhibition 展览
C. extension 延长
D. extinction 灭绝
正确答案：D
译文：在可预见的未来，许多物种可能会濒临灭绝，包含三分之一到三分之二现存物种。
