(a)by words, either spoken or written, or by signs or by visible representations or otherwise, knowingly promotes or attempts to promote, on grounds of religion or race, disharmony or feelings of enmity, hatred or ill-will between different religious or racial groups; or

(b)commits any act which he knows is prejudicial to the maintenance of harmony between different religious or racial groups and which disturbs or is likely to disturb the public tranquility,