do cg will clear all graphics drawn.
do cg
It will clear all graphics drawn with pens and dots, but
it will not clear text written with write, and it
will not clear turtles made by new Turtle. See
ct and cs to clear text or
clear the whole screen.
Saying cg by itself will not do anything, because
our language only runs commands with at least two words:
you need to use do cg.