Нужно подобрать к словам одну из отрицательных приставок in,un,im
Able,clear,helpful,pleasant,known,credible,capable,
complete,accurate,patient,perfect,possible

UnableUnclearUnhelpfulUnpleasantUnknownIncredibleUncapable

unable, unclear, unhelpful, unpleasant, unknown, incredible, incapable, incomplete, inaccurate, inpatient, imperfect, impossible