Bonjour,
Réponse :
a. This is Bob. Bob is my best friend.
→ This is Bob. He is my best friend.
b. Anita and Kate are sisters. Anita and Kate are twins. Anita is blond. Anita looks very different from Kate.
→ Anita and Kate are sisters. They are twins. Anita is bland. She looks very different from Kate.
c. My mother has got short, blond hair. My mother is very tall.
→ My mother has got short blond hair. She is very tall.
d. Otto is my new puppy. Otto is very cute, very small and very clever! Otto and I love playing together.
→ Otto is my new puppy. He is very cute, very small and very clever! We love playing together.
( Otto est un animal domestique = on peut donc utiliser "he" )