The twelve words below can be grouped into two groups of six according to a certain pattern. Can you determine the pattern and the two groups?

INK

EAR

YOU

ERE

SOU

READ

UNDER

STEAL

FOUR

RASH

GROW

ROUGH

 

Answer:

 

Six of the words can be preceded by TH, and six can be followed by TH to make new words:

 

THINK---------------------EARTH

THERE                           YOUTH

THREAD                        SOUTH

THUNDER                     STEALTH

THRASH                        FOURTH

THROUGH                    GROWTH