expensive → more expensive → the most expensive 

thick → thicker → the thickest

friendly → more friendly → the most friendly

fine → finer → the finest

thin → thinner → the thinnest

difficult → more difficult → the most difficult

warm → warmer → the warmest

wise → wiser → the wisest

easy → easier → easiest

wonderful → more wonderful → the most wonderful

sunny → sunnier → the sunniest

fat → fatter → the fattest

long → longer → the longest