Alice, your parents were really anxious about you. You ______ home without a word. [      ]

A. mustn't leave

B. needn't leave  

C. couldn't have left  

D. shouldn't have left

YJ19平准器劈刀盘上有一些凹槽，这些凹槽可使吸丝带上的某些区域多保留一些烟丝，若切刀切在该区域，则会在烟支端部形成紧头位置，减少（）的产生。