Sound part isn't seen on the timeline.

I was editing a project and while I was doing something, suddenly the voice  part of timeline has gone. It isn't seem but when I play the video, I can still hear the voice. Also in the the other sequences of the project, there is still sound part on the timeline. It is not exist for just one sequence. I have been trying to fix it for hours. Please help me. Also I added the photo of timeline which there is no sound.