how to clear the output in gnuplot buffer

[emacs25]

when i run "run-gnuplot",i do something like this:

gnuplot> plot sin(x)

then i get a image in the buffer,but when i use "clear" command ,the output is still here,including codes and a empty image.

how should i do to remove all the output except leavng a sngle prompt at 1st line of the buffer?