Pseudostratified columnar epithelium looks like it has multiple layers because the nuclei are at different heights, but it is actually a single layer of cells. The defining feature is that every cell rests on the basement membrane, even though not all reach the lumen. This combination—one cell layer with varying cell heights, where all cells contact the basal surface—creates the characteristic pseudostratified appearance. This tissue is commonly found in the respiratory tract, where it is often ciliated and contains goblet cells to help move mucus. The statement describing a single layer with tall cells and every cell touching the basement membrane best captures this key idea, distinguishing it from true stratified epithelia (which have multiple layers) and from simple columnar epithelia (where the single-layer arrangement is more uniform and all cells typically reach the lumen).