6. Kirill hasn't bought a present for his friend. Anton hasn't any idea what to present to his friend.

Решение:

В предложении два отрицательных факта: Кирилл не купил подарок, и Антон не знает, что подарить. Для объединения этих двух отрицательных утверждений используем neither ... nor.

Kirill hasn't bought a present for his friend. Anton hasn't any idea what to present to his friend. → Neither Kirill nor Anton has bought a present for his friend.

Ответ: neither ... nor