The central heating system of this office building is down and several workers ______ it right now.

China's present environment situation is from bad to worse and if we _________ now to protect the environment, we’ll live to regret it.

Cathy went to the hospital alone. If she had told me about it, I _____ with her.

By the time we arrived at the railway station, the train _________. As a result, we missed the train.

As we know, dry wood _____ fire easily.

–Jack is ill in hospital.
--Really ? I __________ him right now.

— The floor is dirty.
— Yes. It _______ for two days.

My sister_____ Tony for ten years next year.

Do you know a concert _____ in our hometown next month?

Tom，as well as his friends，______ going to visit the Great Wall this winter vacation.