________ is known to all is that effective measures should be taken to deal with the problem of the over­exploitation of our resources.

Have you ever dreamed of staging a concert, ________ thousands of people are applauding and appreciating your music?

He is _______ here as he was at home. 

This painting is so valuable that it is rather difficult to calculate _______ its price would be if the museum _______ to sell it.

________ all over the hills and around the lake are wild flowers of different kinds.