He turns deaf ear to his parents, ________ many times they have pointed out his weaknesses.[ ]

A. whatever  

B. whichever

C. however  

D. whenever

从粮食中检出一种污染物，不溶于水，可在紫外光下产生蓝色荧光，加碱处理后荧光消失。这一污染物最有可能为

A．B(a)P
B．AFBl
C．亚硝胺
D．铅
E．BHT