75. What it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust _______________ a solid globe.
76. It was not immediately obvious that water _______________ to the development of life.
77. So whether life will continue on the earth for millions of _______________ will depend on whether this problem can be solved.
78. The fish are not sharks or killer whales, but favourite eating varietieslike cod and skate which grow to _______________, sometimes as much as twelve feet in length.
79. He said that someone might be spying on the station and the pilot was ordered to _______________ the strange object.
80. Those who failed to get in _______________ disappointed, as many of the artistes who should have appeared did not come.
76.settled into
77.was to be fundamental
78years to come
79.unnatural sizes
80.keep track of
81.need not have felt