下列各组物质相互作用，生成物不随反应条件或反应物的用量变化而变化的是( ) A．

外障

若-1，a，b，c，-4成等比数列，则a·b·c的值为（    ）。

Many people prefer paper bags to plastic ones because they are environmentally  ________. [      ]

A. welcome  

B. useful

C. friendly 

D. helpful

The opening day of Expo 2010 Shanghai China we have been forward looking to_____ to arrive.

A．being

B．be

C．is

D．will

漂白或未漂白其他苎麻纱线