已知信号<img src="https://static.zxtiku.com/wangke/imgs/topic/ce63ca577ca947a648516081a33d029c.jpg"/>，试确定<img src="https://static.zxtiku.com/wangke/imgs/topic/0c3a9218b74c145324a9051c9ac2a856.jpg"/>信号为零的值（）<br/> A、<img src="https://static.zxtiku.com/wangke/imgs/topic/bb5ccbce6123b2fb58ad7d9c30da3985.jpg"/><br/> B、<img src="https://static.zxtiku.com/wangke/imgs/topic/431a18c64e913135adb98ebf396447e3.jpg"/><br/> C、<img src="https://static.zxtiku.com/wangke/imgs/topic/1a4dafacce7af66722340f4e4317bd5d.jpg"/><br/> D、<img src="https://static.zxtiku.com/wangke/imgs/topic/adc3d9ee6abb765be24d783822683b91.jpg"/>