What I did is:
1) I draw a ellipse;
2) I offset it;
3) I draw two lines passing though the original ellipse and the offset ellipse;

This question is:
I can trim the original ellipse, but
I cannot trim the offset ellipse.

I can't trim none of the ellipses

1.- In Menu "Settings/Drawing Settings" palet "Entity Creation" choose in "change setting for " Ellipse and click in "Create Ellipses as Polylines".

2.- Redraw ellipses and offset.

3.- trim Ellipses