Вопрос:

Open the brackets, put the verb in the correct form in the sentence: “You can’t leave her alone. You need (to help) ... her.”

Ответ:

You can’t leave her alone. You need to help her.

The verb need is followed by the infinitive with to in this sentence. Перевод: «Ты не можешь оставить её одну. Тебе нужно помочь ей».