Задайте вопрос к подлежащему. начните вопросы со слова who.

1. she can work.
work?

2. he has got three brothers.
three brothers?

3. they could roller-skate.
roller-skate?

4. she invited bob to the party?
bob to the party?

5. he likes to write letters.
to write letters.

1. She can work.

Who can work?

2. He has got three brothers.

Who has got three brothers?

3. They could roller-skate.

Who could roller-skate?

4. She invited Bob to the party?

Who invited Bob to the party?

5. He likes to write letters.

Who likes to write letters?

Просто надо вместо подлежащего писать слово who (для людей и иногда животных) или what (для неживых предметов).

Только помните, что who/what всегда согласуется с глаголом в един. числе. Пример:

We are waiting for you.

Вопрос к подлежащему выглядит так:

Who is waiting for you?