I love this textbook series! I never found them on Chinese language books websites, so in the end I got them in China. This series covers the HSK vocabulary from Beginner till Advanced level (I also own the two volumes of the Beginner level but they’re not relevant to me anymore). It’s alphabetically sorted (which is a bit of a downside, imagine learning six characters pronounced “fan” in a row and trying not to confuse their meanings) and every page on the left lists around 10 to 15 entries and on the right side are the corresponding exercises. The first exercise is about filling in the blanks with the words you just learnt. The second exercise often shows two or three words that can be easily confused as they have similar meanings but are used differently. The third exercise shows a few sentences and you have to choose the corresponding usage explanation. It also comes with an answer key at the end of each volume.