Many species of animals are in danger of ________ due to the pollution these days. [ ]

A. dying out      

B. dying away

C. dying off  

D. dying down

对于两种证券形成的投资组合，基于相同的预期报酬率，相关系数之值越小，风险也越小；基于相同的风险水平，相关系数越小，取得的报酬率越大。 ( )