4) She ________ her fingernails, but she grew out of it.

Выполним задание.

4) She ________ her fingernails, but she grew out of it.

В данном предложении необходимо использовать конструкцию "used to" и глагол "bite".

She used to bite her fingernails, but she grew out of it. - Она грызла ногти, но отвыкла от этого.

Ответ: She used to bite her fingernails, but she grew out of it.