Change the structure as in the example. This is my chair. – This is mine. 1. This is his car. - ____________________________

За my, your, her, his, its, our, their всегда стоит существительное. 

 Mine, yours, hers, his, its, ours, theirs ставится, если существительное опущено. Формы надо запомнить.

1. This is his car. - This car is his.

2. This is their dog. - This dog is theirs.

3. This is her key. - This key is hers.

4. This is your sandwich.- This sandwich is yours.

5. This is my cup. - This cup is mine.