在一个不透明布袋中装有红、黄、白三种颜色的乒乓球各一个，这些球除颜色外其它都相同，从袋中随机地摸出一个乒乓球，那么摸到的球是红球的概率是（ ）。
It was not until dark _____ he found _____ he thought was the correct way to solve the problem. [ ]
A. that; what
B. that; that
C. when; what
D. when; that
在什么情况下冷冻单元需要紧急停车？
