Many environmentalists think that carbon dioxide is _______ for the global warming, which affects billions and billions of species across the globe.[ ]

A. blamed  

B. to be blamed  

C. to blame 

D. blaming

耐磨铸铁具有高而均匀的硬度，在生产上常采用（）的办法来获得。

A．高温退火

B．热轧

C．激冷

D．冷变形强化