I don’ t mind _____the door.
| A．you open | B．your open |
| C．your opening | D．yours opening |
_______ provides many hours of air for astronauts in space.
| A．An air tank | B．A power pack | C．A helmet | D．A space sleeping bag |
We are wondering ________ we can prevent people from polluting the earth.
| A．who | B．that | C．whether | D．what |
The gravity on Mars is only about ________ of that on Earth.
| A．1/2 | B．2/3 | C．1/8 | D．3/8 |
It is hard to imagine what life __________ in 100 years.
| A．will like | B．will be like | C．likes | D．might like |
My friend John insisted that he had seen ______ alien the day before.
| A．a | B．an | C．some | D．any |