B. Max's favourite activity is ... 1) having fun in the park. 2) hiding under the sofa. 3) playing tug of war with other dogs. 4) sleeping on the sofa.

Решение:

В тексте указано: "He enjoys playing with balls in the park. It's his favourite activity." Из предложенных вариантов, "having fun in the park" наиболее полно описывает эту активность.

Ответ: 1) having fun in the park.