They are swimming in the river now (in the lake). Задать вопрос: общий, альтернативный, специальный, разделительный/с хвостиком, вопрос к подлежащему.

1. общий

are they swimming in the river now?

2. альтернативный

are they swimming in the river or in the lake now?

3. специальный

where are they swimming now?

4. разделительный

They are swimming in the river now, aren't they?

5. к подлежащему

Who is swimming in the river now?