D. Our friends asked my parents to give them some money ...

Решение:

В тексте сказано: "It was an expensive operation. Our friends did not have enough money to pay for the operation. They asked my parents and they gave them some money." Это означает, что друзья попросили денег у родителей Ника, чтобы оплатить операцию ветеринару.

Ответ: 1) to pay the vet.