晶闸管从导通恢复阻断的条件是什么？
参考答案：晶闸管从导通恢复阻断的条件是：晶闸管的电流小于维持电流，阴极电压断开或使其反向。
有红、黄、蓝、黑四种小球各若干个，每个人可以从中任意摸出两个．那么，需要多少人同时摸球，才能保证至少有2人摸的小球颜色相同？
Stella was disappointed to find her new plan _____ and fell into great depression.[ ]
A. set down
B. turned down
C. calmed down
D. written down
