The scientists ________ on the new medicine for two years. They will succeed in no time. 

Please come to my party if you ____ free tomorrow.

I’ll do it better if the teacher _______ me ten more minutes.

—What a clean and bright classroom, isn’t it?—Yes, it’s always clean and bright because it       every day.

-Be careful! You might fall into the water. -Thank you. I____.I______ so close to the pool.