Choose the suitable words to complete the sentences.

Choose the correct option.

I need new sheets; these [one|ones] aren't clean.

If you buy two bars of chocolate, you get a third [one|ones] for free.

"Have you got a blue shirt?" — "No, but I've got several green [one|ones]."

Don't put on those socks. The woollen [one|ones] are much warmer.