The letter C is one of the easiest letters to create. First step is to create a new vector layer named C.
On C layer, draw ellipse in middle of canvas. Size it similar to A & B by using grid.
Ellipse ToolColors: Black outline, fill color of your choice. I will use blue.
Tool options: Ellipse, Show Nodes, Create on Vector, Line Style Solid, Width 3, Anti-Alias checked.
Pen Tool-Edit Mode: Select ellipse, right click, convert to path.
Because the ellipse preset shape already has the 4 symmetric nodes we need to create a C, we just need to push the right side node toward the left until shape looks like a C. Except the C will need a bit of fine tuning. Move the top and bottom nodes further to the right and turn the control arms until they point vertical. Now lengthen the control arms for all 3 nodes to fatten up the letter.
Adjusting the nodes may have distorted the size of the C somewhat. To resize, use Pick tool to select C and drag edge of bounding box to desired height and width.
Deselect C and hide visibility for C layer before creating D layer.