a) New York City is the biggest and the most populated city...

(big : adj court 'the + adj + est // il est terminé par

consonne-voyelle-consonne, on double le 'g')

(populated adj long : the most + adj

b) Washington DC is the most visited city...

c) Los Angeles is one of the sunniest cities in...

adj 1 ou 2 syllabes terminés en "y" => y devient i

d) Alaska is the largest and the coldest state...

large => largest

e) The Mississippi river is the longest river in...