| 31 × | biology | 5 × | elements | 1 × | ecology | ||
| 19 × | chemistry | 4 × | java | 1 × | humanbody | ||
| 14 × | spelling | 4 × | geography | 1 × | dates | ||
| 13 × | english | 2 × | genetics | 1 × | interviews | ||
| 11 × | medicine | 2 × | classification | 1 × | taxonomy | ||
| 10 × | periodic-table | 2 × | accounting | 1 × | music | ||
| 9 × | anatomy | 2 × | symbols | 1 × | physics | ||
| 7 × | programming | 2 × | javascript | 1 × | nodejs | ||
| 6 × | botany | 2 × | mnemonic | 1 × | shopping | ||
| 6 × | mathematics | 1 × | immunology | 1 × | database |