Tom, clean up the broken glass _________ someone walks on it.
We watched, amazed as fire _____ on the outside of the spaceship as the earth’s gravity increased.
Walking does need a bit of practice _____ gravity has changed.
They multiplied and filled the oceans and seas with oxygen, _____ encouraged the later development of early shellfish and all sorts of fish.
_____ is even more important is that as the earth cooled down, water began to appear on its surface.
It was not immediately obvious _____ water was to be fundamental to the development of life.