Week three exercises are really exciting the more you do them. The more cylinders I did, the more confident and faster I executed the following groups. I made the effort to rectify the ends of the ellipses to improve symmetry along the long axes, on each. If you fantasize drawing anything from coffee mugs to castle turrets, this exercise will do the trick.
Note: I took snapshots, of the above, under sunlight conditions. They were all drawn on white, basic printer paper. Indoor lighting tends to appear dimmer and requires good knowledge using curves (Color menu) in GIMP.
I use the Brightness/Contrast (Colors menu) feature to sharpen the edges.