Scientists say human activity contributes to climate change, but they do not agree on the rate_______ climate change may be developing.

A．with which

B．with that

C．at which

D．at that

回火可消除钢材淬火时产生的内应力，使其硬度降低，恢复塑性和韧性。回火温度愈高，钢材硬度下降愈多，塑性和韧性等性能均得以（）。