The letter k and digraph 'ck'

C and k join each other for the digraph 'ck'   

lick        sack        sock           suck
pick       pack        pocket        stuck
trick       back        shock                   luck
sick       Jack                   knock                     yuck
quick     quack      rocket         duck
wicket    racket     hockey        luck
prick      knack           lock                            muck
kick       whack     block           truck