Level 1. RIG, RED, DIG, RIDE, DIRE, RIDGE
Level 2. READ, ROAD, DARE, DEAR, ADORE
Level 3. TRUE, TREK, TURKEY, TYRE
Level 4. THROAT, TORT, TROT, THAT, TART, OATH
Level 5. WHIT, WITH, WHIG, WHET, WEIGHT, TWIG
Level 6. SURF, SURE, FUSE, SUFFER, USER, RUSE
Level 7. VICE, AVID, CAVE, ADVICE, IDEA, ACID, DIVE
Level 8. SLIM, SLIP, LIMP, LISP, SLIMY, SIMPLY, IMPLY
