____ + ____ = ____

某化学兴趣小组按照课本实验方法（如下图），做木炭与氧化铜反应的实验时，发现很难观察到紫红色铜的生成，却往往有暗红色固体出现。他们决定对这个实验进行探究和改进。

【提出问题】暗红色的固体是什么？如何选择合适条件，使木炭还原氧化铜的实验现象更明显？

【查阅资料】铜有+1 和+2 两种化合价，通常情况下，氧的化合价为-2，碳的化合价为+4 或-4。

阅读下面短文，从短文后各题所给的四个选项（A、B、C和D）中选出最佳选项。

    Look at the car. It is Mr Black's car. It doesn't work now. Mr Black is under it. He is repairing it. Mrs Black is near the car. She is helping Mr Black. A girl is in the car. She is Kate, Mr Black's daughter. Who is the boy in the car? He is Jim, Kate's brother. It is Saturday today. They don't work. They want to go to Zhongshan Park. They all look worried.