下列说法正确的是 [ ]

A．反应条件是“加热”的反应一定是吸热反应

B．升高温度可使化学反应速率增大

C．用KClO₃分解制O₂时，如果不用MnO₂，反应就不能进行

D．炼铁时，增加高炉的高度可以使CO完全转化

What does the speaker say about the artists in the United States during the Great Depression().

A.Many artists lost faith in the value of art.

B.Many artists were forced to take jobs in other fields.

C.Many artists moved away from large cities.

D.Many artists in the United States moved to other countries.