First of all, there is no requirement to draw, draw corners and make auxiliary lines with pens (black pens) or pencils. So you can use a pencil or a pen. There are requirements on the thickness of pens in the admission ticket.

Secondly, according to your own level, when you need to use a pen as an auxiliary line for geometry problems, you can clearly know that it is ok to use a black signature pen as an auxiliary line; Draw with a pencil if you are afraid of making mistakes.

I suggest: when drawing, draw evenly with a pencil and draw a little heavier, as long as you can see clearly.