质量衰减系数μ／ρ，质量能量转移系数μtr／ρ和质量能量吸收系数μen／ρ三者之间的关系是（）

A.μ／ρ>μtr／ρ=μen／ρ

B.μ／ρ>μtr／ρ>μen／ρ

C.μ／ρ<μtr／ρ<μen／ρ

D.μ／ρ=μtr／ρ>μen／ρ

E.以上都不对

Many of the world's plants and animals have already___   , and several other species are endangered.     [ ]

A. died away            

B. died out    

C. died down          

D. died off