— What’s up, Dave? — The meeting is almost over, but Henry hasn’t yet.
_______ provides many hours of air for astronauts in space.
We are wondering ________ we can prevent people from polluting the earth.
The gravity on Mars is only about ________ of that on Earth.
It is hard to imagine what life __________ in 100 years.
My friend John insisted that he had seen ______ alien the day before.