Bonjour,

Réponse :

1. Her hair is too long. ( Ses cheveux sont trop longs )

  The girl's hair is too long. ( Les cheveux de la fille sont trop longs )

2. Its legs are too short. ( Ses pattes sont trop courtes )

   The dog's legs are too short. ( Les pattes du chien sont trop courtes)

3. His head is too big. ( sa tête est trop grosse )

  The boy's head is too big. ( La tête du garçon est trop grosse )

4. His legs are too long.

    The boy's legs are too long

5. Her arms are too long.

   The girl's arms are too long.

6. His arms are too short.

   The boy's arms are too short.

Explications :

Tu dois utiliser soit un possessif ( her/his/its), soit un cas possessif