2. Скажите, что их несколько. (§ 2) his friend — his friends; 1. his pencil — his ...; 2. my book — my ...; 3. your horse — your ...; 4. his cake — his ...; 5. your house — your ...

Правило: чтобы образовать множественное число существительного, обычно добавляем окончание -s.

1. his pencil — his pencils
2. my book — my books
3. your horse — your horses
4. his cake — his cakes
5. your house — your houses

Ответ: his pencils; my books; your horses; his cakes; your houses.