Решение:
Для заполнения пропусков необходимо преобразовать слова в скобках так, чтобы они грамматически и лексически соответствовали контексту.
- (FRIEND) → FRIENDS: Horses have lived with people for centuries. They are FRIENDS and clever animals...
- (POSSIBLE) → POSSIBLE: Farming was POSSIBLE without them.
- (DIFFER) → DIFFERENT: Nowadays crops are grown and transported with DIFFERENT machines...
- (STRESS) → STRESSFUL: ...where people's life is STRESSFUL and tense.
- (TRAIN) → TRAINING: ...a professional TRAINING can teach you how to ride a horse.
- (COMMUNICATE) → COMMUNICATE: If you really enjoy COMMUNICATE with these animals...
Ответ: FRIENDS; POSSIBLE; DIFFERENT; STRESSFUL; TRAINING; COMMUNICATE.