| tough(adjective, characteristic, difficulty, burden, problem) |
| unmanageable(adjective, characteristic, difficulty, hardship) |
| stubborn(adjective, characteristic, difficulty, hardship) |
| exigent(adjective, characteristic, burden, problem) |
| nice(adjective, characteristic, difficulty, hardship) |
| problem(noun, adjective, characteristic, hard, difficulty) |
| quantum physics |
| abstract(adjective, characteristic, difficulty, hardship) |
| abstruse(adjective, characteristic, difficulty, hardship) |
| ambitious(adjective, characteristic, difficulty, hardship) |
| argumentative(adjective, characteristic, difficulty, hardship) |
| awkward(adjective, characteristic, difficulty, hardship) |
| backbreaker(adjective, characteristic, difficulty, hardship) |
| baffling(adjective, characteristic, difficulty, hardship) |
| bearish(adjective, characteristic, difficulty, hardship) |
| bewildering(adjective, characteristic, difficulty, hardship) |
| bold(adjective, characteristic, difficulty, complication) |
| boorish(adjective, characteristic, difficulty, hardship) |
| bothersome(adjective, characteristic, difficulty, hardship) |
| carking(adjective, characteristic, burden, problem) |