People like to live a life full of ________ and there are _______ of life styles available for people to choose in the modern world.     [ ]

A. a variety; a variety  

B. varieties; varieties  

C. a variety; varieties  

D. variety; varieties

下列说法中错误的是                                                                          （   ）

A．通常蔗糖和淀粉都不显还原性

B．纤维素分子是由葡萄糖单元组成的，可以表现出一些多元醇的性质

C．油脂是热能最高的营养物质

D．铜盐可以使蛋白质产生盐析