Which ionospheric region is closest to the Earth?

The ionosphere is divided into multiple layers or regions, alphabetically named D, E, and F, based on their altitude. The sequence starts from the lowest altitude moving upwards. Therefore, the D region is the lowest layer of the ionosphere, sitting closest to the Earth at approximately 60 to 90 kilometers above the surface. The E region sits above the D region, and the F region is the highest. There is no 'A region' in the standard classification of the ionosphere, making it a completely fabricated distractor.