下列信号中属于功率信号的是_____。<br/> A、<img src="https://static.zxtiku.com/wangke/imgs/topic/65b02ca2e4dfc51e6c54acda5c47e04d.jpg"/><br/> B、<img src="https://static.zxtiku.com/wangke/imgs/topic/b8bb60c7d8a20561087b68daf99edb9a.jpg"/><br/> C、<img src="https://static.zxtiku.com/wangke/imgs/topic/50ca99e663dba2d6bf53390cbb528f4b.jpg"/><br/> D、<img src="https://static.zxtiku.com/wangke/imgs/topic/78506f4b5b71b8390c716a87dac7a6dc.jpg"/>