We do have trained people, but the problem is how to organize them, and ____their enthusiasm.
This produced a chain reaction, _______ made _______ possible for life to develop.
The thought they couldthe whole continent was exciting.
_________ life will continue on the earth for millions of years to come will depend on __________ this problem can be solved.
--May I open the window to let in some fresh air? -- __________
__________ is even more important is _________ the earth cooled down, water began to appear on its surface.